HARRY POTTER star Daniel Radcliffe has an uncommonly respectable habit - he insists on calling his film director 'Sir'.

The 16-year-old actor, who shot to fame playing the part of the boy wizard in Jk Rowling's blockbuster series of films, blames it on his school rule which encouraged pupils to call their teachers by the name.

Courteous Daniel says, "I'm not sure why. I don't come from any, even vaguely militaristic background.

"I think it's just that I'm younger than him.

"At my last school my teachers always seemed to insist upon being called Sir.

"I always think of the director as a captain of the ship. So it might be something to do with that."