Yet Smith has achieved massive international recognition for her Professor McGonagall in three Harry Potter movies in the past four years.

"Well, yes, for a younger audience," she says. "Not that I do a vast amount in those films. Of course, it can absolutely stun children if they suddenly connect you. I suppose I'd be noticed a bit more if I walked round in that hat all the time. Sometimes, I'm in a restaurant and I can see them thinking, 'Hmmm, I know who that is', and when they work it out, they go completely to pieces." Then what happens?

"Then you sign all sorts of things for them and say, 'No, I'm afraid I can't turn into a cat'."

She makes the same point Judi Dench was making recently: about it being hard for actresses that there is no Mrs Lear.

"I'm lucky to have got McGonagall,' she says. "I suppose there's Mrs Malaprop and things like that. Joan says you develop into grotesques, which is what these parts are. It's not a moan, it's a fact."