CM: I believe the only complaint that’s ever made about Sherlock is that there isn’t enough?

MG: I believe the whole of China just said that, to the Prime Minister! I was very tempted to Tweet, as Mycroft, “I am afraid Mr Cameron does not speak for her majesty” [laughter].

BC: Oh, one can but dream.

[Five giggly minutes or so of online fan-fiction being read out and discussed here, before the questions were opened up to the audience].

Audience member 1: What was it like returning to the characters after two years away?

MF: For me, it’s a little bit like slipping into an old coat and feeling very familiar with it. I love the familiarity of the world and the writing and working with Ben and the newcomers on set. It just feels like something that we really enjoy, and saving our own presence, we’re quite good at it now. We love giving it to you [laughter].

BC: It was a lot of fun to do, bike rides and bungee jumps and bonfires and

Audience member 1: Operation?

BC: That game of Operation was really, really good fun and we get as much fun as you do, hopefully when we first read the scripts. So, if we’ve done our jobs half right from the audience reaction then I know that’s transmitted, but it begins with these two boys here [Moffat and Gatiss], but it’s a lot of fun to be back.

Audience member 2: The fake solutions presented there, did you come up with those yourselves, or were they directly taken from fan speculation?

MG: Certainly, there was a collision of things around the idea of Derren [Brown] being involved.

SM: It was very early when we talked about starting that way, it was when all the theories were starting to kick off, and we just thought we’d make up a bananas one of our own.

MG: There’s a reference to the laundry truck, which is a famous one but impossible, and if you notice, he says, in the second of the thirteen solutions, he says ‘there’s a system of Japanese wrestling’ and it gets cut off, which is actually Conan Doyle’s ludicrous solution to the end of The Final Problem.

BC: The paving slabs, as well, from an episode of Jonathan Creek…

MG: Yes, Alan Davies said he knew how we’d done it!

SV: It was interesting seeing everyone watch it though, because it started off and you see people gradually losing confidence. [laughter].

MG: There was a round of applause for the squash ball! Everyone going, ‘yes, I knew that’. An extraordinary one was that rhododendron pollen, which was in Reichenbach, is a drug that will simulate the effects of death, it’s like a coma thing, and it’s a total coincidence, that. People ran with that one for ages.

CM: That was why he was crying apparently, because it was a reaction to a drug. Have you thought about doing it again, it’s not conclusively wrapped up, there’s still some mystery around it. Could you come back and do another version?

SM: I think that would be a little bit uncreative.

CM: Keep it going forever. Every six years, ‘this is another way we could have gone’.

Audience member 3: The episode was a lot of fun, but when it went to a Terrorist plot, I found myself having a fear reaction. Did you think about, tonally, what it would do to bring that into it? It was very tastefully done and had wonderful emotional pay-off but did you think about that at all?

SM: We do aim for tasteful terrorism [laughter]

MG: Terrorism has been with us for a very long time, it’s ever-present. A friend of mine who saw the episode a couple of days ago, and actually I think it’s a bit of an odd coincidence, we made it a while ago and really what’s happening at the moment with Snowden and everything, there’s a lot of interesting stuff embedded in there about the secret state and some of it is just what’s happening at the time, really. I just thought it was a lovely idea of a Bonfire Night plot and essentially, it’s just a way of having a great big bomb. But you have to be aware of these things. It’s odd, Martin had a line about the IRA getting restless again, which they have just done.

BC: Our version is in the twenty-first century. It should be about the reality that is part of our lives.

MG: You’ve got to say, it’s always meant to be a bigger version, it’s a slightly more lurid world. I remember there was a pompous letter to the Radio Times after the first series saying ‘How can you have a 7 foot 2” assassin called The Golem?’ Because it’s Sherlock Holmes! We’re still within workable parameters in our world, without things becoming too ludicrous, but yes, you have to be aware of these things because there are taste issues.

SM: Did you mean about the reality of that?

Audience member 3: I’m from Boston, so it’s maybe a little bit of a raw nerve. I had the same reaction to the opening sequence in Star Trek Into Darkness, because it’s real and it happens all the time.

MG: We’ve had terrorism longer than Sherlock Holmes, that’s the truth of it.

BC: We’ve had terrorism in our underground as well, so it wasn’t treated lightly.

CM: Is there anything too dark that you wouldn’t do? Do you bear in mind the audience and when it’s going out, you’d never do an eleven o clock show, was it always going to be that slightly post watershed?

SM: We’re aware that kids do like watching it, so we make sure that it’s alright for them. I wouldn’t characterise it a children’s programme at all, but we know that children watch and we wouldn’t want them to be excluded from the audience, and that wouldn’t be right for Sherlock. Sherlock Holmes isn’t like that, those stories have always appealed to children.

MG: It’s the spirit of adventure, isn’t it?

SM: It’s murder by luminous dog!

SV: It was actually made for pre-watershed.

MG: CBeebies, originally [laughter].

Audience member 4: Mark, is it different writing a character you then have to play?

MG: It is difficult. It’s a bit easier really, because I find it easier to learn my own words. It is fun. In the second series, the only scene in The Hounds of Baskerville with Mycroft, I don’t say anything, but it was required for this episode. I can still say [launches into a few lines in Serbian with relish – applause]. The only Serbian I’ll ever know.

SM: There’s a whole line, and it’s quite an important line, in His Last Vow, which was never written down, it was just agreed between us, we just said ‘no, it’s fine, Mark’s going to say that’.

CM: What was that line?

SM: Not saying.

MG: There’s a certain baddy at the end, with his round spectacles you may have seen…

CM: Can you say anything at all about what’s coming up?

MG: Well episode two is called The Sign of Three, in which John Watson and Mary Morstan get married.

CM: Is it at all like your own wedding, could you get the old dresses out and save the BBC a bit of money?

MF: My dress doesn’t fit [laughter]. Not really, no. Much more eventful, this one. Much more eventful, in really entertaining thrill-riding ways.

MG: It’s not about the canapés!

SM: Episode three is based on a story called Charles Augustus Milverton, so you can go home and read that right now. He’s a really interesting villain, a really hideous villain, I think the only villain that Sherlock Holmes genuinely hates. He doesn’t really hate Moriarty, apparently [in reference to the almost kiss in The Empty Hearse]. He absolutely hates Charles Augustus Magnusson, played by Lars Mikkelsen, doing an absolutely brilliant and terrifying turn as our new villain.

CM: Can we just confirm that Moriarty is definitely dead? As dead as someone in Sherlock can be, or actually dead?

SM: They did not fake suicide at each other. Imagine how stupid you’d feel if you bumped into each other [mimes, ‘what, you too?]. He’s dead.

Audience member 5: Your version of Sebastian Moran is quite a step away from a sniper. Could you tell us about that?

MG: Sebastian Moran is the sort of baddie in the original story of The Empty House and he’s Lord Moran in there, it’s just a tiny glancing reference really. We talked a lot about this, Doyle had it himself, Sebastian Moran is assuming quite big proportions in the world of Sherlock, but really he’s just Moriarty’s henchman, there’s not much more to it. Doyle, I think, had the same problem of him not being Moriarty, so rather than just have a villain at the stake of it, we just didn’t do it really. Like The Empty House original, the most important thing is getting them back together and the Doyle story is a very, very flimsy locked room mystery in which you just can’t wait for it to happen and in a sense it’s the same sort of thing happens really. It’s just a wonderful excuse to have a great time.

Audience member 6: What were Benedict, Martin and Mark’s favourite scenes to film in this one?

MF: We’re kind of spoilt for choice really. I did enjoy filming in the tube train, I thought that was fun.

Audience member 6: Where you were mournfully staring forward?

MF: Just me doing that [crosses arms]. No, I liked the end, I did enjoy doing that with the bomb going off, I thought that was good fun.

MG: That tube train, the bomb at the end, was designed by Arwel Jones, our amazing designer, it’s not a real train. We couldn’t get a real tube train, so it was incredible.

BC: [To Mark] Do you want to go next, because I’m still thinking. I liked our deduction scene, actually, I liked doing that with you, that was really good fun.

MG: We do play that in real life, and get nothing right.

MG: My favourite scene in it, actually, is the reveal of Sherlock in the restaurant as the waiter and the look when Martin finally turns around, it’s just fantastically played, and the range of boiling rage and shock and horror and grief, and then when he’s suddenly exposed, like Poirot, ‘this was a bad idea’ [laughter].

BC: Honestly, the deduction scene, I loved doing that, and also the reunion, although there was a lot of pressure on it to get it right. I liked the one in the tube as well, that was a fun day. Despite what it may look like, being bungeed is a lot of fun, falling onto an airbag is a lot of fun.

Read our spoiler-filled review of The Empty Hearse, here.