Audience member 3: Can I just congratulate Louis [Moffat] on his marvellous role as young Sherlock [applause]. Was it fun to add in young Sherlock?

SM: It’s a feature of updating it is that if you’re portraying Sherlock accurately, as he is in the original stories, in his thirties, then a person in their thirties in the modern world would still be in touch with their parents. The parents should be there, and how marvellous were they? Once you’ve got the parents in, and you’ve got the sibling rivalry in you start to think, well, what was little Sherlock like? You just want to see those things, it’s part of updating it.

Audience member 3: Does that mean we’ll get to see baby Mycroft? [laughter]

SM: Baby Mycroft is just Mark Gatiss in a CGI reduction, he’s never been any different [laughter]. I’m pretty sure that’s true of Mark as well, he was just a mini Mark in a three-piece suit with an expression of distaste [laughter]. Don’t tell him I said that!

Audience member 4: Should we expect a similar wait for the next series or are you tempted to try and get it done in a year this time? [‘Oooh, get you’-style noises and laughter from the audience]

SM: What have you been doing? How many Sherlock Holmes films have you made? [laughter] I’ve made nine!

Audience member 4: It’s just that everybody’s waiting for it.

SV: We’re working on it, we’re working on dates. It’s dates.

SM: Obviously Benedict and Martin are apparently in some movies? [laughter] I know, who cares about movies? I agree with you, I agree with your thinking there, who cares about their movie careers? But they apparently are doing films so we’ve got to schedule around that but we’ll get them made as quickly as we can.

AA: [stage whisper] Martin’s free from April.

SM: Heaven knows what she actually means by that. Bad news for Martin! [laughter]. Tremendously available, possibly homeless! [laughter].

Audience member 5: I was just wondering about the creative decision to bring Moriarty back. I’m thrilled, but you were very adamant he wasn’t coming back.

SM: Because I’ve always given this grand commitment to telling the truth! [laughter]. You don’t know what’s going on there. You don’t know what’s going on there. We know what’s going on there but we’re not telling you…for bloody ages! [laughter]. It must be hell watching this show. Obviously, we enjoyed that we get to see more of the wonderful Andrew Scott as Moriarty. [Applause].

NH: There was a marvellous intake of breath across the whole cinema when his face turned around.

And a sob when Benedict kissed the girlfriend…

SM: ‘But it’s alright, he was treating her badly’?! [laughter]

Audience member 6: A section of The Sign Of Three that everyone is going to love forever is the stag do. How much was scripted and how much was improvised, and which was your personal favourite bit?

SM: I don’t know if I ever want to own up to the fact that it’s scripted – it is – but we didn’t script the wonderful performances. It was scripted, we didn’t just get them drunk [laughter]. They wouldn’t have turned up, they’d just have gone off somewhere! We loved doing that, it was a light bulb moment and we were sitting there thinking ‘what is Sherlock Holmes like drunk?’ and immediately you think, ‘that’s a terrible crime! He would never be drunk’ but then you think, ‘hang on, he’s a substance abuser, of course he’d be drunk. He does everything else, why wouldn’t he be drunk?’ And it’s never been done, so we had this brand new thing. What is Sherlock Holmes like drunk? Well he’s like a pissed Sherlock Holmes [laughter]. It did work very well. We were very, very happy with it.

Audience member 6: Little things like Martin doing the high five thing. Was that scripted?

SM: I’m struggling to remember it. [Amanda Abbington does a good impression of the moment being described] There were loads of good bits. There was a lovely moment also – probably my favourite line in it – where Benedict says ‘Apologies on behalf of my…thing’ and it’s because Benedict in that moment forgot his lines and just said ‘thing’ and Mark and I went ‘Oh that’s good, let’s keep that in’ [laughter]. It was lovely.

AR: Benedict finds it very hard to remember lines, he told me in previous interviews

SM: Well if you see the number he has!

AR: Just generally he finds it hard, so this has got to be a living nightmare.

SM: It is. It’s tough, but there are very few parts in television that require you to learn so much stuff that is not intuitive, you can’t really paraphrase it. You’re simulating the thought processes of a genius so we’re making leaps that are not immediately easy for those of us mortals who play the part so it’s a tough one.

AR: Martin learns his lines like that [quickly] doesn’t he?

AA: Oh, it’s pathetic [false scorn in her voice, laughter].

Audience member 7: When I watch the episodes I feel you did your research with the fans on the internet and Tumblr and so on and maybe interacted with the fans?

SM: I really didn’t. I’ve been on Tumblr once a long time ago and it seems to be a place where people who really want to kill me gather [laughter]. I don’t know why that put me off! I thought ‘No, it’s enough that lunatics know my name, I don’t have to hear them talking about me. Sorry, so I don’t know. No, we don’t get our plot-lines from Tumblr.

Do you think that the future of television is more a combination of an interaction with fans?

SM: It’s not how it works, it truly isn’t. The creative response of fans is amazing, it’s extraordinary, and it’s not an exaggeration to say it’s the cradle of the next generation of television and fiction producers. It’s hugely important, but it’s a one-way thing. What happens is – and I was part of this, I am part of this – is that you see something you love, you start doing your own version of it. Then you start disagreeing with the actual version and think ‘my version’s better’, and then you discover you’ve made something entirely different and you go off and do your own thing.

I find it exciting and thrilling and wonderful that you get that creative response to a TV show. It’s how I began – I responded to Doctor Who and Sherlock and look how far I’ve come! [laughter]. I find that exciting but no, interaction with the fans is not how it works because in the end they’ve got to cut loose from the mother ship and do their own thing, and they will, they will. I think it’s incredibly exciting but no, we don’t interact with the fans apart from saying ‘hello’ and how much we love them.

NH: It acknowledges it.

Audience member 8: It’s great that the BBC can show 90 minutes without any commercials, however, in the markets you’re going into, you get commercials all over the place. Do you have any control over where the breaks come?

SM: Interesting. Do we, Sue?

SV: Where breaks come? No. If we needed to cut something down we could cut it down here.

I presume you’ll have to do it for Dave one day? [laughter]

SV: We try not to look at it.

SM: We try to end every scene on a cliff-hanger. Every scene ends with somebody going ‘And that’s what they were supposed to think!’

SV: That’s not where they cut it, probably!

SM: You do see that thing where they cut the scene in the bloody middle and you think, come on, we’ve given you four hundred and twelve decent cliff-hangers, how did you miss it? I think it’s a shame if they don’t do it well, because I have no objection – me personally – to commercials turning up during the show as it’s an opportunity to have a whopping great cliff-hanger. I quite like that.

Audience member 9: In terms of this episode, it’s probably the most non-linear of the three so far this season. When you’re constructing a story like this, do you basically plot it from point A to point Z and then fold bits back on themselves as you go along?

SM: To be honest, I think I would say that The Sign Of Three was the most non-linear. We don’t even know if we saw the events in the right order even in the flashback. In terms of how you do that, you just work it out. I remember the writers on The Sign Of Three sat and worked out that we wanted the spine to be the speech, that we’ll cue up that story there and leave it hanging, and go back to the speech, cue up the next story, then we go back to the resolution of that story. It’s designed – perhaps successfully or unsuccessfully is up to you – to look clever.

Things that are designed to look clever secretly aren’t that clever, because we know the story and putting it in the wrong order isn’t that much of an effort. There’s only one sequence where we move out of straight narrative logic in His Last Vow, I wrote it that way and we all wondered if we’d just cut the Christmas scenes into the right sequence, but it didn’t feel right, you sort of wanted to go forward into the future and then find out how they’d got there. If you put the work in, it’s not as hard as it looks. It’s designed, as I said, to look clever. In the case of a show that celebrates the cleverness of its hero, the show being itself clever is correct. If it wasn’t a show about a clever man, you wouldn’t want it to be like that. It’s a show about a clever man, so make the world look complex, yet clear – he hoped! You may be thinking ‘It wasn’t clear at all!’ [laughter] but that’s the ambition. I don’t know if that ramble was of any use at all, I’m sorry.

Audience member 10: Do you have any dreams for season four that you would like to do, any casting or plots that you would love to bring into next season if budget wasn’t an issue?

SM: If budget wasn’t an issue… I never really worry about that, my wife worries about that [laughter].

Rather excitingly Mark and I, for no particular reason, just got out of the rain and sat at the top of the production bus – whereas the actors get these marvellous caravans, we go and sit at the top of a double decker bus that becomes our office – and we sat with all the accountants and we just started talking about what we could do in the future, and we plotted out the whole of series four and five just in one day.

SV: Then the accountants said you couldn’t afford it [laughter]

SM: They know all about it, they do. They heard us. So we have got plans, yeah. But our plans don’t tend to be ‘let’s blow up the world’ or ‘let’s cast the most famous person in the world’, it tends to be what exciting twists and turns can we add to this, and I think we’ve got some crackers. The ideas we thought of that day I think we the best we’ve ever had. There, bigging it up already! [laughter].

Audience member 11: Because Lars was such a fantastic character, I know you have to keep to the storylines of the books as a backbone, but were you not tempted to not kill him off and you could have had a fantastic series four with a Lars/Moriarty tag-team. The two best criminal minds ever.

NH: Is he dead?

SM: At some point, don’t you think they’re going to sit in 221B and say ‘Nobody ever dies!’ [laughter]. ‘How are we supposed to investigate murder if they all get up again!’ Lars was brilliant but the first idea was to honour the story and kill him.

LM: You never know, do you?

SM: You never know! [laughter] An endless procession of ‘Did you miss me?’ ‘And me!’ ‘And me!’ Phil Davis will be so happy, back driving that taxi!

The Sign Of Three was the first time that all three writers were credited on the episode, did that change the writing process? Did it benefit from having three minds on it, that story? Also, who signs off and says it’s done at the end?

SM: We sort of segmented the episode into the different bits we were doing. It was Steve [Thompson’s] first draft, he did a couple of drafts, then Mark and I came in with Steve and I focused a lot on the wedding and the speech and Mark focused a lot on the mysteries, and Steve focused a lot on the stag night actually so it just worked around that, but we all did everything. When do you sign it off? When they need it! That’s the reality.

NH: It’s never signed off.

SV: When it sounds round.

SM: Yes. But I delayed the tone meeting for His Last Vow because I hadn’t finished the script. I kept phoning and telling them ‘I’ll be there in an hour, I promise’ and they’re all sitting at a table saying ‘He hasn’t finished it’.

Read our spoiler-filled review of His Last Vow, here.