The story of Sherlock Holmes, on the surface, is about detection, but in reality, it's about the best of two men who save each other - a lost, washed-up war hero and a man who could end up committing murders instead of solving them. They come together. They become this perfect unit. They become the best friendship ever, and they become heroes. That's what we fall in love with, not Sherlock on his own. No one can love that man on his own, but Sherlock Holmes and Dr. Watson - the best friends ever.

I wouldn't mind removing all the mistakes I have made. That would be exhausting and take forever. Honestly, it's one of the spells of my life that has been the most perfect. Not because I did the job perfectly, because of course I did it very imperfectly, but because I enjoyed it so much. What would I change? I complain a lot. I whinge, I more or less communicate in levels of complaint so I wish sometimes I didn't just spend all my time saying, 'I'm working so hard, what do I get in return for this?'.

Peter Capaldi, will always be Doctor Who. You retain the title forever. Ask your predecessors, they all think they're the real one. I've had Sunday lunch with Peter Davidson and David Tennant and they're eyeing each other like, 'It's me!

Sarah Jane Smith was everybody's hero when I was younger, and as brave and funny and brilliant as people only ever are in stories. But many years later, when I met the real Sarah Jane - Lis Sladen herself - she was exactly as any child ever have wanted her to be. Kind and gentle and clever; and a ferociously talented actress, of course, but in that perfectly English unassuming way.

If anyone said to me 'invent a new monster so we can sell more toys', I'd kick them out of my office.

Never ignore a coincidence. Unless you're busy, in which case, always ignore a coincidence.

When writing comedy, you have to have the confidence to believe that there is only one type of relationship in the world, and we are all having it, that all men behave in the same way and so do all women.