"I'd wanted to work on stage here again, and to work with Michael (Grandage, director), for a long time. We'd discussed projects - an Ibsen, I think - but the timing has never been convenient.

For me the hardest thing to negotiate is time away from my family. But this series of Doctor Who was shot during my daughter's spring break, so she could come over for that. And Luise Miller coincides pretty much with her summer holiday. So I was able to prepare myself psychologically for her going back to school, thinking: six weeks is really hard but it will be all right because she'll be with me for the summer again.

If Michael had offered me this during term time I don't know if I could have accepted it. That said, this is what I do. I wanted to be an actor to perform plays, to work with other people to create something. If you think of creativity as a muscle that has to be exercised, there isn't that much opportunity to do that in television.

... it’s totally the end of Doctor Who for me, too. I can’t imagine anything would bring me back, and they’re done with Rose.

They’ve got this great new set up with Matt Smith and Karen Gillan and it works brilliantly. So there’s no way in the world it will happen again for me – well not for the foreseeable future.

Both Belle and Rose have been brilliant for my career, but I don’t know yet if they might become curses some day. They haven’t been so far, but who knows? The problem with something like Secret Diary is that you could end up getting endless sexy scripts and a long line of sexual predator parts, which you could tire of.

It’s not something I want to keep doing over and over again. And I got a lot of stick about it, too. Playing a prostitute doesn’t go down well with everyone, surprisingly. But the role took me into the American market, which is fantastic.

I had a bit of a mad year, to be honest, and was sick of the sight of myself by Christmas, so God knows how everyone else felt. In my defence, scheduling is a curious beast and it fell out that two things I'd made the previous year (The First Men in the Moon and Worried About the Boy) ended up being shown slap-bang in the middle of my History of Horror documentary series for BBC4. On that subject I must take this opportunity to record how fantastic it is that there's still a place where a passion project (as that series most certainly was) can be so championed and encouraged. Equally, that documentaries as startling and oddly moving as The Young Ones and as rich and strange as The Dancing Boys of Afghanistan still have such a valued place.

Speaking of scheduling, it's worth saying that when Sherlock was scheduled to air in the traditionally dead summer slot it seemed like very bad news. It's a measure of how differently we now watch shows that this didn't prove to be the case. Whether catching up on iPlayer, recording on our Sky boxes or downloading our favourites, overnight ratings are ceasing to have any meaning. But you mustn't get me started on ratings or I'll start singing "The King is in the Altogether" and we'll be here till Christmas.

I remember being called in once. The producer said, "We’ve got a major problem. We’ve had letters from 12-year-old boys saying the physics couldn’t work. In the future, can you guarantee the physics will work"?

Mr Fisher decided to get in touch with scientists working at a Cambridge astronomy centre, near where he lived, and asked if he could talk some ideas through with them.

It turned out they were Doctor Who mad.

The experts helped him not only come up with a way for the Creature in the Pit to threaten an entire planet with a neutron star but also a way to stop it.

They said "that’s perfectly simple too. Just wrap it in tin foil".

Oh yes, the Daleks. Actually, they aren’t going to make an appearance for a while. What? Yes, we thought it was about time to give them a rest. There’s a problem with the Daleks. How come? I thought they were invincible. They are the most famous of the Doctor’s adversaries and the most frequent, which means they are the most reliably defeatable enemies in the universe. They have been defeated by the Doctor about 400 times. Surely they should just see the Tardis approaching, say, ‘Oh. It’s him again’, and trudge away.

Daleks: I was talking about THIS series. Stand down.