This page is currently for early comments/thoughts/news regarding Season 4. Nearer to broadcast time, it will become the page for the first episode of the season.

It's a sure sign that they're currently filming the new episodes. As soon as the Sherlock crew go out on the streets, the weather turns shockingly bad. We've had snow in central London twice this week!

When will Hartswood learn that they should film the series in June?!

Well hopefully it's better than season 3 because I can't see how it could have been much worse...

Shhh, don't say that out loud, or someone will endeavor to show you how.

One of the Setlock photos which I didn't manage to avoid has already got me worried.

Whited-out spoiler (highlight to read):
I don't know what's worse - the sight of Sherlock and the Watsons apparently out on a case with John carrying the baby strapped in front of him, or the thought that once again this "story about a detective, not a detective story" is likely to go out of its way to break our hearts when either the baby dies or Mary has to disappear and takes their daughter with her.

I wish the show would revert to crime-solving and adventure and excitement and move away from its progress towards an extended episode of EastEnders.

First trailer here.

The Three Words (i.e. one word for each episode as a clue for what might happen) for Season 4 were released some time ago but I forgot to post them here.

The word for episode 3 seems to be especially spoilerific, although knowing the writers it might also be a Scarlet Roll Mop and turn out to be Molly's new cat or a village in Suffolk or something. But look away now if you don't want to be even potentially spoilered.

(la-la-la add in lots of space before saying them)






So the three words are:

Thatcher / Smith / Sherrinford

Knowing how unlikely it is that the producers would give away such a huge clue so early on, it does seem unlikely that Sherrinford will be The Other One in the sense of being either Mycroft's or Sherlock's long-lost twin brother (or even sister). Someone on another forum had the idea ... oh, wait, I think it was me! ... that s/he might end up being James Moriarty's twin instead.

More ideas and links to Doyle canon for the first two names in particular can be found here.

Since then, it has been pretty much confirmed that the character played by Toby Jones will be Culverton Smith, who appeared in the canonical story The Adventure of the Dying Detective. The second episode's title has now been announced as The Lying Detective.

John made a blog entry called “The Six Thatchers” just before the Christmas when Scandal was happening. His blog entry – obviously based on the canonical The Adventure of the Six Napoleons – is here. It’s unlikely that Gatiss has forgotten this, so perhaps Season 4 will start with/include some flashbacks to earlier cases, stuff that happened even before the Fall? Either that or these previous “disappointingly simple” cases (as described by Sherlock and reported by John) will come back to haunt them.

Season 4 will begin on Sunday 1 January 2017 both in the UK and the USA.

Link to the second trailer, and a transcript of the spoken words here.

The first proper clip from Season 4 was shown on The Late Show with Steven Colbert at the weekend. A link to the Youtube video, plus a transcript of the spoken words is here. There are no major spoilers in it.

Link to the second clip, plus a transcript, is here. If you're avoiding all spoilers, this one reveals baby Watson's name.

This is the first ep I watched the day it actually aired. It was on a bit late in my area, probably why I didn't catch it before, but I'm still surprised I remembered.

Anyway, The Six Thatchers started off a bit slow but overall I thought was an excellent episode, with an intriguing mystery sub-plot. However, this being a nitpicking site, I noticed a couple things...

SPOILERS!!

When Sherlock and AJ were fighting near the pool they crashed through a window and land a good distance into the water, despite the window and pool being several feet apart.

The scene at the aquarium begs some scrutiny I think. Mary is a highly trained black-ops agent yet her response to Sherlock getting shot at is to jump in front of the bullet, facing the direction it's coming from. Instead of pulling Sherlock out of the way or blading her body so that the small caliber of the Walther PPK hits her in the arm, she gets hit in the chest. Maybe TPTB wants the show to return to a duo but there are better ways to do that IMHO.

Finally, why wasnt there more of an inquiry done after the Georgian incident? Sure they wanted to cover the whole thing up, but I don't buy that Mycroft didn't want to know the whole story.

I’ve finally surfaced from writing the transcript!

Even after going through the entire episode with a fine-toothed comb, I’m still not sure what to make of it. The style felt very different from previous seasons. I’m wondering if this is due to the new director’s method of filming. It’ll be interesting to see whether the style becomes more recognisable in the next episode, which is directed by the same person who did His Last Vow. There’s another new director for the final episode.

Mycroft shows the “beyond top secret” videos in a room which has a floor to ceiling window looking into the room at the video screens.

If Sherlock really is still high after his overdose on the plane and isn’t just playing the little kid in order to embarrass his brother, Sir Edwin’s people faked the footage of Magnussen being shot incredibly quickly. Or is this days later and Sherlock is still using? There’s no reason why the fake footage would be made before they knew that Sherlock was going to stay in the country, so it can only have been made after Jim’s message went out. I suspect, therefore, that Sherlock’s just being a brat to make his brother squirm in front of important people.

If Vivian wasn’t allowed to minute the meeting, what was her purpose for being there? Shouldn’t she have been sent from the room (or not even allowed in in the first place), and Lady Smallwood given the choice of how much to tell her later?

On the other hand, Mycroft gives four code names. Assuming that one of those isn’t allocated to Sherlock himself, why is Vivian so important (despite being ‘just’ a secretary) that she gets her own code name? Actually, I reckon that she’s very much Lady S’s right-hand woman and is therefore privy to many secrets.

Sherlock spent a week in solitary confinement after shooting Magnussen. Even if it was some swanky government place rather than a normal prison, there would still have been warders/security people who saw him during that time. Can they all be hushed-up?

I love how at one point Sherlock tosses a piece of ginger nut biscuit towards his mouth and spectacularly misses and then has to scrabble beside his lap to retrieve it.

John types a blog entry entitled “221Back!” explaining what’s been happening lately. Once again the people who wrote the text need thumping. Part of the entry says, “If I’m not changing nappies, I’m buying nappies.” But he said in the previous paragraph, “I’m going to be a Dad,” and moments later we see that Mary is still pregnant. Surely he hasn’t got a life-sized doll and is repeatedly practising nappy-changing on it, wasting money on packs of nappies which he then throws away after each change?!

It was lovely to see DI Dimmock again!

Sherlock’s look of horror when he looks down towards Mary’s legs in the back of the car is hilarious! Some fans have captioned a screenshot of that moment, “This is a man who has never seen ladyparts before.” However, from the angle at which he was sitting in relation to Mary’s legs, either he was simply appalled because she had pulled her dress up so high that he could see her ladyparts, or the baby’s head was actually out at that moment.

Why is Molly one of the godparents? I don’t imagine that either John or Mary have spent much time with her.

I love the way that, just before he asks Sherlock to be godfather, John holds his hands wide and stares upwards as if asking himself, ‘Why am I doing this?!’

According to a brief behind-the-scenes documentary, the production team managed to get “a few” of the guests from the wedding to return for the christening. However, only one couple is visible throughout the scene.

I adored Sherlock’s tetchy conversation with ‘Watson,’ eventually revealing that he was talking to Rosie, not John!

On the bus, John gets two messages from Sherlock but neither has his trademark ‘SH’ at the end. It isn’t that he’s stopped doing it because he adds them to later messages to the Watsons.

When John gets off the bus, you can clearly see his left ear and he doesn’t seem to be wearing the daisy at that point. Strangely, the flower is more visible the second time we see the same moment later in the episode.

In the flashback to Charlie Welsborough’s burned skeleton in the car, it seems clear that the bones are covered with the remnants of some burned/melted material. However, Greg says nothing about this when telling Sherlock about the incident (although Sherlock then asks about the seat covers in a spectacular and rather unbelievable piece of deduction).

After Greg and John have been snarking about how Sherlock’s no different to a fractious baby, Sherlock stops at the bottom of the stairs and, for his last line in that scene, he is reflected in the mirror in the hall. A lot of the fandom didn’t realise that and kicked up merry hell about why his parting was on the wrong side of his head.

Why does Sherlock make a big thing of pretending not to know who Margaret Thatcher is? I know that he’s playing for time but he makes a huge deal of it, and we know that he knew who and what she was when he was trying to work out Major Barrymore’s password in Hounds.

I like the way that Sherlock congratulates the Welsboroughs on their OCD.

David Welsborough says, “How anybody could hate [Thatcher] so much, they’d go to the trouble of smashing her likeness ...” Where the bloody hell has he been hiding all these years?!

Sherlock’s startled reaction to the balloon floating above John’s chair was hilarious!

The bloodhound that played Toby was apparently useless, not liking walking on tarmac and frequently refusing to move at all for long periods. The scene where they’re standing by the phonebox waiting for Toby to do something was written on the hoof during the filming because of the dog’s stubbornness. When we see a close-up of Mary being led through the market by the dog, it’s actually a member of the film crew at the other end of the lead, holding it low to the ground and walking backwards off-camera! There’s a behind-the-scenes clip of Amanda in Borough Market pulling on the dog’s lead with all her weight while he refuses to budge, until she eventually falls over backwards.

When Sherlock is back at Craig’s, who is looking at the orders from Gelder & Co, there’s a street sign on the floor behind them reading ‘Pinchin Lane.’ This is the name of the road to which Watson in the Doyle story The Sign of Four is sent to collect Toby the dog. I wonder if the sign was made in this show with the intention of putting it on the wall outside Craig’s house but maybe the production crew weren’t allowed to, so they stuck it in Craig’s room just to save completely wasting it.

There has been much fandom meta over the fact that Mary and John are lying on opposite sides of the bed to how they were seen in previous episodes. A lot of this relates to the fact that they’re first seen reflected in a mirror and so look as if they’re on their ‘usual’ sides. Indeed, there has been much meta about the frequent use of mirrors in this episode, prompting all sorts of bizarre theories. Me, I wouldn’t be surprised if it was simply a directorial choice that has no particular relevance at all.

Craig the computer hacker says, “Time’s a great leveller, innit? Thatcher’s like – I dunno – Napoleon now.” This is a nod to the original Doyle story “The Adventure of the Six Napoleons” on which this part of the episode is based. Many of the names from that story – Gelder & Co, Barnicot, Harker, and Sandeford amongst others – come from the original story. And in that story it is indeed the Black Pearl of the Borgias which is hidden in one of the Napoleon busts.

One has to assume that Sandeford knew that Sherlock was in his pool room unless Sherlock pulled some kind of ‘false car seat’ trick, though it seems strange that Sandeford left him in the room alone with his daughter for a while. But it would also explain why Sandeford didn’t come running when the window to the pool room smashed.

How does Sherlock know what John said to Mary at his parents’ cottage? He was outside smoking with Mycroft at the time. Is this a sign that none of what we’re seeing in this episode is really happening; or is it just really shoddy writing? Maybe that flashback was for our benefit rather than was an actual memory of Sherlock’s but if they wanted to show the pen drive being burned, they could have just shown that, because surely John told him what he did later.

How did Sherlock know that he would need armed police at the house? The intruder may have killed Orrie Hacker but he did that with a knife and Sherlock couldn’t have known for sure that he would also have a gun. (Though I suppose it’s possible that Sandeford heard all the noise and called the police, but again why did they arrive armed?)

For some odd reason, the hostage-takers talk in Georgian at the embassy but in Russian while chasing Ajay (one of my beta team knows the difference between the two languages).

Shocking directing: when Ajay finds the six Thatcher busts in the pottery workshop, they’re all standing up. When he stuffs his memory stick into the open base of one of them, suddenly that bust is laying on its front. Also, he then stands it up. As soon as anybody picks it up, the stick is going to fall out, not get conveniently baked into the bust. In the original story, the pearl was pushed into the wet plaster. Shown as it is in this episode, even if the stick itself is wedged, the chain’s likely to drop down. Additionally, the guy with the teeth is right behind him and knocks him out as soon as he turns from the bust, and so he must have seen what Ajay did and would have investigated.

At least it now makes a little more sense why Mary was carrying her AGRA memory stick when Sherlock ‘outed’ her in His Last Vow. But if the device contains all the others’ details, was she really willing for John to read it, even believing they were dead? And why did neither she nor Ajay have passwords on the sticks? And it still makes no sense why she told John that “AGRA” was her initials.

Ajay sees the shadow of someone in another room being beaten or flogged. The man has long floppy hair, which sent one of my beta team into flailing hysterics remembering Sherlock with long floppy hair being beaten in The Empty Hearse. Even though these new events happened six years ago, I joined in with the flailing. However, during the two flashbacks at the embassy in Tbilisi, we briefly see both Alex and Gabriel (well, we do if, like me, you go through that footage split second by split second) and both of them have short hair. Even if a lot of time passed before we saw the torture scene, why would the hostage-takers allow Alex’s hair to grow but kindly keep cutting Ajay’s? The error is compounded by a brief flashback of the shadowed figure being shown when Ajay later tells Mary how he heard Alex’s back break.

When Mary approaches the door to the church vault on her way to meet Sherlock, graffiti on the door reads “GwJ.” Apparently these are the initials of the son of Arwel wyn Jones, the Production Designer.

Did Mary suspect that Sherlock might be ‘up to something’ when she went to meet him in the vault, or does she always carry chloroformed paper with her?! And what kind of arsehole starts to feel funny the moment he touches it and then sniffs it deeply?!

Mary says in her letter to John that she’s travelling purely on the roll of dice, but then goes somewhere where she has hidden fake ID. She may well have fake IDs hidden all around the world but how likely are the rolls of three dice to send her to any of them, especially when the overlays suggest that she’s using the dice’s numbers to go to random places in an atlas based on those numbers?

Mycroft rattles off information about the city of Agra and Sherlock asks him, “What are you, Wikipedia?” Mycroft smugly replies, “Yes.” Delightfully, he really is, because the information he gives is quoted verbatim from the Wikipedia entry!

How the heck did Mary manage to masquerade as the flight attendant without any of the other attendants noticing?

I loved Sherlock sitting on the floor playing Happy Families with Karim!

John says it was his idea to put a tracker in the memory stick. So Sherlock must have told him before he (Sherlock) went to meet Mary at the church. And John let him and didn’t insist on going too?

The coordination between Sherlock and Mary is awesome after Ajay’s arrival. I love the way the two of them trade off their only pistol so seamlessly. I would have loved to have seen the two of them work together more in the future.

Lady Smallwood finds that her pass doesn’t work, and behind her a man in a suit and a uniformed security guard approach. I started to write the man as being Sir Edwin but then frowned and said, “No, that’s not him,” and so wrote him as a ‘suited man.’ Then one of my beta team said, “That’s Sir Edwin.” I checked the end credits and there’s no credit for any other man, so I changed it back to Sir Edwin but even after I took a screencap of him at the beginning of the episode and put it beside the later footage, I’m still not totally convinced because he looks similar but a lot older. Maybe the strain of learning that his colleague is a traitor aged him?! Either that, or he’s got a less healthy twin brother. Except that it’s never twins. ;-)

The mystery redhead (credited as ‘Elizabeth’ in the end credits) gives John her number and later he texts, “Hey,” to her, which she repeats in her reply. Shouldn’t her reply have been more along the lines of, “Who dis?” or, “Is that you, flower boy?” (Some people online are speculating that none of John’s text conversations are actually with that woman.)

This time, when Mary gets out of bed and heads for Rosie’s room, she says, “I’m coming,” instead of “Mummy’s coming,” like she did last time we saw this scene. If it’s not a massive clue that none of this is really happening, I can only assume that they filmed the scene a few times and then buggered up the edit.

When John gets off the bus looking at his – as yet – unsent message, an extra sitting on the bus behind him is very obviously mugging into the camera!

When Vivian shoots Mary, blood spurts out of the wound. This contradicts what Mind Palace Molly told Sherlock in Vow: “It’s not like it is in the movies. There’s not a great big spurt of blood ...” This has led to much online speculation that Mary faked her shooting and death, and some maniacs people ... actually, no, some maniacs have even suggested that John shot her from behind. Also, even though it made me cry, the whole ‘living just long enough to give a goodbye speech’ bit seemed rather unrealistic, but then this is drama and it’s often not true to life.

Apparently quite a lot of people laughed at the gutteral noises coming from John after Mary died. I found them appallingly realistic.

The sight of John once again being forced to walk across a graveyard broke my heart.

One of the takeaway menus on Mycroft’s fridge is for a restaurant called Reigate Square. Again, this is a nod to Conan Doyle canon. Additionally, one of the other menus has an elephant on the front. Arwel wyn Jones has a fondness for incorporating elephants into scenes. Certain elements of the fandom are convinced that these repeated ‘elephants in the room’ are Proof!Dammit that Sherlock and John will eventually become a couple.

In a long shot of the Watsons’ living room while John is pacing around it, we see that the kitchen is beyond it. This made me go back to check the footage of Many Happy Returns and the flat has a different layout there. The kitchen is beyond the living room but in Thatchers the front door is at the front of the living room. In MHR we see that corner of the living room and there’s no front door there and, when the doorbell rings during Sherlock’s ‘Happy birthday’ video, John looks towards the kitchen, not towards the front of the house. Also it makes no sense why John and Greg come out of the kitchen in MHR and then shake hands. Surely they would have shaken hands at the front door, wherever it may be?

Sherlock asking Mrs Hudson to say ‘Norbury’ to him if she thinks he’s getting cocky is from the Doyle canon, although in that case Holmes asked Watson to say it.

Sherlock’s face is a study in heartbreak when Molly tells him that John doesn’t want him around.

When Sherlock sits in the back of cab, possibly reading John’s note, we get a voiceover of Mary from her video. When we saw her onscreen earlier, she said, “When I’m ... gone – if I’m gone – I need you to do something for me.” In the voiceover, she phrases it, “When I’m gone – if I’m ... (and then she breathes out a shaky breath and the next word is tearful) .... gone – I need you to do something for me.” Again, I suspect that Amanda did that speech more than once and the editor buggered up. Of course, it hasn’t stopped certain elements of the fandom theorising that Something Is Up.

In case anybody switched off or changed channel as the credits rolled, afterwards there’s a brief shot of Mary on the DVD looking into the camera and saying, “Go to Hell, Sherlock,” before the disc shuts down. Many people have pointed out various towns in the world which are called Hell, and that makes far more sense than Mary giving him such an emotive case and then being rude to him.

The soundtrack for this season, already available to pre-order, will have two discs rather than the one each for the previous three seasons. I’m kind of surprised, seeing as there wasn’t much new music in this episode, instead re-using lots of music from previous episodes. The only new music which I actually noticed was during Charlie Welsborough’s death, during Mary’s ‘roll of the dice’ travels and during her death.

Somehow I should not be surprised that Thatchers refers to none other than Margaret Thatcher herself.
The episode title and the story is based loosely on the short story The Adventure of the Six Napoleons and I can only wonder what Thatcher’s reaction would have been being compared to Napoleon like this.
Funny that Sherlock pretended not to know who she was!
Mary’s past crops again with someone from her past profession Ajay turning up now wanting her dead.
Ajay is played by Sacha Dhawan and he had played the first Doctor Who director Waris Hussein in An Adventure In Space and Time written by Mark Gatiss. Gatiss also wrote The Six Thatchers as well as appearing as Mycroft.
Fascinating the flashbacks to Georgia.
Charlie says that travel broadens the mind. As Gatiss is both a Doctor Who writer and long time Doctor Who fan he no doubt got that line from the Doctor Who serial The Hand of Fear.
At a bus stop there is a poster of Toby Jones. No doubt this is an Easter Egg to his appearance as Culverton Smith in the next episode The Lying Detective.
Very sad that Mary gave her life to save Sherlock.
Cheeky of the late Mary giving Sherlock a video with what Moriarty says on the disc and interesting the case that Mary gives to Sherlock.

Charlie says that travel broadens the mind. As Gatiss is both a Doctor Who writer and long time Doctor Who fan he no doubt got that line from the Doctor Who serial The Hand of Fear.

Or he could have got it from the fact that it's a well-known proverb in common use?

"Or he could have got it from the fact that it's a well-known proverb in common use?"

I would agree with that if it was someone who was not familiar with Doctor Who. Occam's Razor.

Gatiss was 10 years old when Hand of Fear was shown so it seems more likely that he encounter this saying from watching this story than anywhere else and he had been watching Doctor Who from at least the original run of the Pertwee era.

Someone pointed out to me that when Mary gets off the boat in Norway, the Norwegian name of that boat translates to "Speckled Band." I'm also told that the boat behind that one is named (in Norwegian) "Lion's Mane." Both are, of course, Doyle canonical stories.

I would agree with that if it was someone who was not familiar with Doctor Who. Occam's Razor.

Occam's Razor would suggest that Gatiss was using a well-known and widely-used proverb independent of it also occurring in not particularly memorable circumstances in a 40-year-old Doctor Who story.

In my earlier post I commented about the different layout of the Watsons' flat. In a scene in the next episode (no spoilers here) we do see that there's a back door as well, leading from the kitchen. It still doesn't make sense why Greg would come to the back door in Many Happy Returns, nor why a back door would have a doorbell, and the new front door is still a continuity error.

Callie - David Welsborough says, “How anybody could hate [Thatcher] so much, they’d go to the trouble of smashing her likeness ...” Where the bloody hell has he been hiding all these years?!

America? ;-)

The AGRA flash drives make no sense. Why would anyone wear into a battle situation something that could be used to kill your teammates?

Why would Vivian waste her shot on a person when she could shoot holes in the aquarium glass and drown all those around her?

Because even multiple shots probably wouldn't do too much damage, and certainly not enough to cause an instant flood. It's not a fish tank - it's a submarine tunnel that's designed to withstand the pressure of a vast volume of water.

And, more importantly, because they'd never been able to afford that kind of special effect.

Yeah, but if someone was pointing a gun at some aquarium glass would you want to hang around down there counting on the glass-making standards of the lowest bidder?

It's just not taking advantage of your surroundings, something you'd expect the character to try to do and TPTB to at least address even if they couldn't afford it.

Those tunnels are not made of glass, they are made of plexiglass, which is much harder to shatter because its long polymer chains will efficiently absorb and contain the energy of an impact. The bullet would at most punch a hole clean through the tunnel's wall instead of breaking it. Of course, I wouldn't expect your average visitor to an aquarium to know that.

I would imagine that Vivian wasn’t suicidal enough to attempt to drown everyone including herself. Until Sherlock arrived she presumably didn’t even know she was under suspicion (though one has to wonder whether she always carried a gun in her handbag, because she could only do so when she wasn’t working; there’s no way she would get it through security at the government offices/MI5/MI6). And it was only after Sherlock started belittling her that she decided to use it just to prove that she wasn’t a nobody; until then she seemed to only be using it as an attempt to get Sherlock to let her go.

The AGRA flash drives make no sense. Why would anyone wear into a battle situation something that could be used to kill your teammates?
Well, exactly. Ajay went to all the trouble to hide his flashdrive, but the rebels captured Alex at the embassy so he didn’t have time to hide his one; and Gabriel appeared to go down under gunfire at the same time, therefore the rebels have got at least one copy and possibly two. It’s unlikely that they would bother to do anything with the information; but in other circumstances the drives could have been incredibly dangerous things to be carrying. And as I said above, the darned things aren’t even passworded!


If only five people (including Sherlock) know that the footage of Magnussen’s shooting was faked, then what about the other people who were in the room at the end of His Last Vow when Mycroft openly said, “My brother is a murderer”? Have they – like the SWAT team – all been silenced/shipped off to important jobs in very obscure areas of the world with no internet or phone connection and no postal service?

John hears an alert on his phone and realises that there are 59 missed calls from Mary. Either he’s been in a very noisy environment or he must have switched it off and then recently switched it back on again. Why didn’t he notice the missed calls then?

Presumably Mary had already been to Hotel Cecil in Morocco and then went out for a while before returning, because this is the only way I can imagine why Sherlock and John knew to go there. It therefore seems odd that Karim says, “Nice to meet you,” to her like he’s never seen her before.

Whited-out spoiler to The Lying Detective; highlight to read:
What exactly did Eurus intend when she masqueraded as the Scottish woman on the bus? Was she trying to break up John’s marriage so that he’d be distracted away from Sherlock? And how would she have found a way to chat him up so successfully if he hadn’t had the flower in his hair? I know it turns out that John’s a bit of a tart, but surely he’s not that easy a pushover?

I’m surprised that Ella agreed to see and counsel Sherlock when John is her client. I don’t know much about the ethics of client confidentiality but I would imagine that – because John will have talked to her about Sherlock during his sessions and so she may know things about Sherlock that he’d probably rather she didn’t – she ought to have declined his request, even if he just barged in and insisted on being seen immediately.

Also her new office is a terribly intimidating place, I would have thought. It looks like a converted church, which would put some people off straightaway, there’s a big gaping chasm down to the ground floor not far away, and a very loudly ticking clock. None of these are conducive to a relaxing atmosphere in which you could spill out all your feelings and secrets!

Rewatching His Last Vow recently, I realised that in the scene when Kate Whitney comes to the Watsons' flat while upset about her son Isaac, again there is no door at the front of the flat and she comes to the back door by the kitchen.

Since I was last banging on about the new front door in Season 4 I've learned that they filmed the scenes in Many Happy Returns and Last Vow on location but - because Season 4 would feature the flat more frequently - they built a set this time. However, adding in a new door where there wasn't one before isn't helpful to continuity, especially when it's not vital to the plot.

Also I suspect that the original building was actually a house. In a Season 4 DVD extra, the Production Manager Arwel wyn Jones gives us a tour of the set and consistently calls it a flat and indeed shows that the bedroom and ensuite bathroom are on the same level as the other rooms. Consequently the staircase at the side of the living room makes no sense at all and Arwel even admits that he's not really sure where it goes. Why not just call it a split-level flat/maisonette? Again, it's not vital to the plot but it annoys the heck out of pernickity nitpickers like me!