Elementary, my dear!

Sherlock, Doctor Who, Game of Thrones... your association with shows that have a cult following is growing by the day.
It's my retirement plan. That's a Venn Diagram of my retirement there!

But it's quite hard to use the word 'cult' anymore, because these shows are now essentially mainstream, aren't they? I think the definition of 'cult' has shifted over the years but yes, these shows have a dedicated following. Doctor Who has a 51-year-legacy for people to obsess about. Sherlock — a lot less. But people are almost always warm and nice. Very rarely do they pin you against the wall.

Doesn't the degree of adulation in itself, though, pin you against the wall?
Not really. It must be hard for Benedict (Cumberbatch) and Martin (Freeman). Although when Steven (Moffat) and I visited Brazil, it was like being in One Direction.

You get a lot of fan mail from China.
Yes, all apparently from the same person. The English is written in exactly the same way. It's extraordinary how uniform it is.

That's you being Holmesian, analysing those letters.
Elementary, my dear!

About your childhood — I've read that your parents worked in a psychiatric hospital and you grew up watching films like Chitty Chitty Bang Bang with the inmates...
That was the first film I watched.
And well, what's written about my childhood is a bit exaggerated. As if the psychiatric hospital is like Batman's Arkham Asylum. But yes, the environment did have an effect. It's just the child I was. I was obsessed with horror and anything dark and strange — much to my parent's despair. But everyone's like that. You always think you're the only one with particular interests until you find that there's someone else who likes the same things you do. So yeah, my childhood sort of fed into my work.

Do you still have that mad scientists' lab in the home you share with (husband) Ian Hallard?
I did. It was a big Victorian house, and we had a spare room. I've always wanted a laboratory since when I was a child. So I built one — it was a red room with gas lights and Victorian chemical equipment. But it was a life lesson. The lab looked amazing, but all I'd ever really do is show it to people, and then I'd just close the door again. I essentially realised that I'd built a folly. That what I'd wanted when I was eight-years-old isn't what I wanted when I was 40. It was a good lesson to learn, although I enjoyed turning back time.

About turning back time. There's huge demand for a Doctor Who and Sherlock crossover. Steven Moffat said that he doesn't have any problem with a crossover, but you do...
He says that because he wants to be the popular one.

But do you see it happening in the future?
I don't want to be a killjoy or Ebenezer Scrooge, but I don't see why people are so obsessed with the idea. When I was a kid, I had no desire for TARDIS to appear alongside the Starship Enterprise. I liked them as they were.
Having said that, I can say that if we did do it, it would disappoint people. Because the image they have in their heads will always be better. It may be possible to do a crossover for comic relief or as a sketch, but that's it.
We should be careful about not giving people everything they want.

Much was said about Doctor Who having a female writer for the first time in seven years. What did you make of it?
I'm not in charge of the show, but I know how hard the production team works to get more of a balance. The problem is that there are fewer women working in TV. So the list of writers who'd be considered would be smaller. Some really good (female) writers were approached, but they either didn't have the time, weren't interested, were less familiar with Doctor Who... it's quite a hard show to write for. So the idea that it's this terribly sexist thing is crazy. It's just a question of getting people to write. People start talking when they don't have an idea of what's going on behind the scenes.
At the same time, writers should be approached only if they are the right picks, not just because people say it's time (to get a female writer). Then it's like ticking boxes and you're not doing it for the sake of the show. If season 10 of Doctor Who would be written entirely by women, it would be fantastic. But I can see why it looks like a boy's club from the outside.

Going beyond Sherlock — you've created your own detective called Lucifer Box.
Yes, I've written three books about secret agent Lucifer Box. The first one is Edwardian, the second one is set in the '20s, and the third, in the '50s. It traces the same character from his 30s to his 70s. Box is a disgraceful, bisexual secret agent.

People are obsessed with the gay undercurrents in Sherlock, but Lucifer Box sounds more interesting.
Yes, the idea was to just put it out there, so to speak (laughs).

Back to Sherlock. Moriarty or Magnussen — who's more nefarious?
Magnussen is based on Charles Augustus Milverton from the novels, but he's a modern baddie. He's basically (modelled on) Rupert Murdoch. He doesn't have a plan, and he's evil in a terribly banal, business-like way. These are the sort of people who wait out wars. He's tweaking strings simply to see what can happen, so he's a different type of baddie.
But Moriarty? He's genuinely, terrifyingly crazy.

Between Molly Hooper, Mary Morstan, Mrs Hudson and Irene Adler, which female character stands out, in your opinion?
Ah. About Mrs Hudson... our version of her has the largest part that Mrs Hudson has ever had. We've given her a back story which is getting more elaborate. We've made her a more maternal figure who regards Holmes and Watson as her boys. Her take on them is that they're slightly naughty children.
Mary Morstan was introduced in just the second Sherlock Holmes novel (The Sign of Four), after which most of the other stories are set in a 'between' time when Holmes and Watson still share a flat. We thought the third season would be a perfect time to introduce Mary, because Holmes was dead and Watson was moving on. She's obviously very different from the Mary in the books.
Mary is a slightly damaged person. They all are. And I think Watson is attracted to her for precisely that reason. They make an interesting team of somewhat fractured people.

You and Steven once said that Molly is the only one who can put Holmes on the back foot.
Molly's interesting because she's not a character from the original stories. She was actually written as a one-scene character, but as soon as we made the pilot, we realised that Louise Brealey (who plays Molly) was brilliant. And I said to Steven, "She should get a boyfriend". That's how the whole Moriarty thing began.
People identify with Molly, because Holmes is blind when it comes to her. But she's now the person he goes to, like when he needed help to fake his death. Holmes knows how much he owes her, so the dynamics have slightly shifted there.
But the important thing to remember is that he's never going to be like us. Holmes has definitely learned more, but it's a bit like Pinocchio becoming a real boy. He doesn't quite get it. He sort of knows why he's making terrible mistakes, and Molly's a part of that.

People keep asking whether Irene Adler will return.
She could, if the story demanded it. In the original story, she and Sherlock don't properly meet. So now it's become this great romance, and she's the woman to him — the woman, depending on your reflection. In the beginning, Sherlock explicitly says he doesn't have a girlfriend or boyfriend. And then he suddenly meets someone who fascinates him. Holmes and Adler have an intellectual attraction. He doesn't understand it. It's like falling in love, but he doesn't know what it is.
It's a misnomer that Sherlock doesn't feel. He just knows how dangerous emotions are, so he's decided — like Mycroft has — that caring isn't an advantage. So when it comes to Holmes and Adler, it's a case of a strange person who's found another strange person.

Speaking of Mycroft. You modelled the character on (British Labour Party politician) Peter Mandelson...
Yes, I even played him in a TV drama.

And it was said that the equation between Holmes and Mycroft in Sherlock was inspired by real life dynamics between you and your brother.
No that's the Daily Mail, and you can tell them to f*** off (laughs). The Daily Mail dug out this interview years ago where I said that I had a happy childhood, but my brother and I, who are three years apart, used to fight like brothers did. They made it into a two-page spread, and it was disgusting. But that was only a tiny thing compared to how they crucify other people. Absolute bollocks. That's not true at all.

That same piece also said that you met Ian Hallard online, and that it was his perfect grammar that attracted you to him. Was that bit true?
That bit was. Well there's more to it than that but yes, I met him online before it was even vaguely fashionable, around 15 years ago. We've been married for six years.

Are you still actively involved with London Lesbian and Gay Switchboard (LLGS)?
Yes, I did a fundraiser for them recently with some friends. Ian's a volunteer and I'm a patron. It's very important to me. The internet may have changed people's perceptions, but you only have to go outside London to realise that you live in a metropolitan bubble and think everything's fine. It's clearly not. So if you can put yourself forward as a positive role model in any way, that's good.

Then there's the thing about gay characters on TV. When it comes to (people's expectations of) Sherlock, the danger is that they project onto it, and then it's more about ticking boxes rather than seeing it objectively. We didn't get into it to carry the LGBT flag on TV.

But Russell T. Davies has this show on Channel 4 called Cucumber, Banana, Tofu which will have a broad spread of gay characters: characters who are camp, not camp, nasty, lovely, one-legged... that's the way to look at it. Otherwise you end up in a situation where you character gets pinned to a wall because he has to be a positive model. It's the problem with the scarcity of gay characters. They end up being exemplars when they should be just like anybody else.
There's a character in Coronation Street played by Anthony Cochran who got flak for being camp — as if some gay people aren't. His boyfriend in the show was not camp at all, so there was a balance. But people didn't like it. It happened with Silence of the Lambs too, with the Buffalo Bill character. There were protests about him being a trans serial killer. It was bizarre. There aren't even many transsexual characters on screen, leave alone transsexual murderers.

You've either acted in or written for a slew of detective and murder mysteries: Agatha Christie's Poirot, Midsomer Murders, Miss Marple... the English whodunnits.
I love them.

You're a big fan of James Bond as well.
Oh totally. I'm so jealous of Andrew (Scott, who'll be part of Spectre)

If all of them — Miss Marple, Holmes, Bond, Barnaby, and Poirot — were in a slugfest...
Slugfest?! (laughs)

...who would win?
Bond, I think (pauses). But Marple would probably poison everyone's tea first.

So Marple, then?
Yes, Marple.