Why did you think Sherlock Holmes would benefit from being brought into the 21st century?
“It seemed to Steve and me that the wonderful characters of Holmes and Watson had become almost literally lost in the fog of the Victorian trappings. Now, as a Victorian/Edwardian obsessive, I’m second to no one in loving that pea-souper atmosphere, flaring gas lamps and all, but by the simple expedient of setting the stories in the present day, it’s been possible to shed a brand new light on Sherlock and John.”

Did you have qualms about the public response to Sherlock?
“We didn’t really, because we were very confident that the modernisation was a simple but very good idea. Obviously, you’d expect a certain amount of resistance but we’ve said from the first that there’ll always be another Sherlock Holmes along soon so if you don’t like our version, don’t fret! Happily, people seem to like ours very much.”

How difficult was it finding your Holmes?
“Very easy! Benedict [Cumberbatch] was our first and only choice. Sometimes, as with a new James Bond, there are a few people you can imagine in such a role. At other times, there’s just an obvious candidate. Benedict has an extraordinary mixture of gravitas and youth, a real Holmesian look and a massive talent.”

As with Doctor Who, you both write and act in Sherlock [Gatiss appears as Holmes’ brother Mycroft]. Can we expect more appearances from you in future episodes?
“I ended up playing Sherlock’s brother through an odd set of circumstances. We’d already talked of him being a sort of Mandelson-like Government manipulator, I was auditioning for Peter Mandelson in the Mo Mowlam film and Steve Thompson (who wrote episode two of our new show) suggested I should play Mycroft. How could I say no? In the stories he’s very fat so we’ve put in a running joke about his diet and yo-yoing weight problem.”

You’ve described working on Doctor Who as the fulfilment of a childhood dream – was there a particular “Jim’ll Fix It” moment?
“Oh yes. I was inside the ‘pod’ that turned me from a 76-year-old mad scientist into a dashingly beautiful (ish) blond youth (ish) and they had to shut the door so it could fill up with dry ice. For a wonderful moment, I was shut off from all the madness of making a TV show and just had a moment to reflect that I was actually, finally in Doctor Who. I got a proper, wonderfully happy chill of pleasure. When I burst out, there are tears in my eyes. It’s all true!”

How do you think Matt Smith compares to previous Doctors?
“I think Matt is amazing as the Doctor. It’s terrific for the series too that he’s managed to make such an impact after the glorious David Tennant. Everyone has their favourites but Matt is already the Doctor for a whole new generation.”

Would you want to play Doctor Who if the opportunity ever arose?
“Listen, I’m Sherlock Holmes’ smarter brother! I’m very content!”

There will be a Dalek at this edition of The Space – eek! Why do you think they remain so frightening, even to modern audiences?
“The Daleks were the secret of Doctor Who’s initial success and remain a vital part of it. No one’s ever been able to quantify why they work, they just do – a design classic with the unforgettable voice and the sheer eeriness of them gliding along like that.”

You made your name with comedy group The League Of Gentlemen – do you think there are echoes of the League in your recent work?
“There are always echoes because the League’s atmosphere was so much based on a collective love of horror and silliness and the macabre and oddness – which is what I do.”

Where do you think your fascination with sci-fi and gothic comes from?
“I bounced off a trampoline when I was four and concussed myself. I’ve never been the same since.”

* Gatiss is joined at The Space by Academy Award-nominated visual effects supervisor Paul Franklin, whose work can be seen in films including Inception, The Dark Knight and Batman Begins.

* Starts 7.30pm, £7.50/£6.50. Visit www.thespace.me.uk