Julie Walters talks about her latest role playing Mo Mowlam in a moving new C4 drama on Sunday, January 31 at 9pm.

What was the physical transformation to Mo like?

“Difficult! My face is the exact opposite of hers – it’s like asking Daniel Craig to play Gerry Adams! Without surgery there is no way I can look like Mo. She was very open-faced with quite a small, prissy mouth for someone who is in no way prissy. The more I realised how well people remembered her, the more frightened I became of the whole thing – and then of course came the baldness.”

You ended up shaving off your hair. Was that tough?

“I started with a bald cap. I didn’t have my glasses on, but I could see the line cap. So I just said: ‘This is dreadful, we can’t do it like this – what if I shave my head?’ I think they were waiting for me to come to the conclusion myself, because it’s a lot to ask someone. I wasn’t completely bald so I looked very, very weird. They wanted to keep hair at the sides for the wigs, so I was bald on the top, had white hair round the side and brown at the back. I looked like a badger!”

How did your husband Grant and daughter Maisie react?

“It was a weird experience. I felt very, very naked. I felt more naked than if I’d had no clothes on. They were very cool about it when I went home the first night and told them I’d shaved it. But when I took the wig off, I ran off to put some make-up on, which is something I never do. I don’t ever wear make-up at home. I thought I looked like Harry Hill, but Grant was really sweet. He said: ‘You know, it’s quite beautiful, really’.”

So what’s next for you?

“It is back to Harry Potter. Mrs Weasley has a lot to do this time. I kill Helena Bonham Carter for a start – and not many can say that. We have a bit of a wand contest, I can’t wait. It will be sad, though, because I’ve watched all of them all grow up. It will certainly leave a void.”