“That was bizarre,” 21-year-old Radcliffe says with a laugh. “I’m very impressed. I do the bra with one hand in the film. I don’t think I’ve ever done that in real life, not successfully.”

“Quite a long time,” he replies, chuckling, when asked how long he had to rehearse the move. “It’s much harder taking it off yourself than it is taking it off other people, I’ve got to say.”

“You have to find out who you are aside from what the media say you are,” Radcliffe said earlier in the day. “If you become reliant on them for a kind of sense of self, then you’re really screwed. We’ve all done quite well in terms of not believing the hype of ourselves, just getting on with our jobs and appreciating that we’re very lucky to be there.”

“One of the thoughts that keeps me grounded is that anyone who got this part would’ve had this reaction. It’s not because there is something miraculously special about me that means Leicester Square’s packed on a Thursday evening in November (for the movie premiere) when it’s been [pouring] down all day. It’s because of the series and anyone who goes into this part would’ve had that same kind of mania around them.”

“I’m playing this guy, where the world around him is all slightly odd and slightly off-centre and he’s sort of the still centre. He’s somebody who finds himself in a horrendous situation in which he thinks he suddenly might have to fight for the life of his son,” Radcliffe said, adding playing the part of a father has only reinforced his desire to have a family.

“I do want to be a dad. I cannot wait to have children. I love kids. It stems from the fact that when I was on Potter during my time there, a lot of people I knew had kids,” he said.

“I start rehearsals in January,” said Radcliffe who has been taking both singing and dancing lessons. “It’s a big singing part but when you compare it to, say someone playing Frankie Valli in Jersey Boys, you sing 29 songs in that part. I think I’ve got nine songs in the whole show and I think only two of them are me on my own... It’s the dancing more than singing that’s totally out of the comfort zone.”