Mrs Doubtfire: A huge success for Columbus

"That was sort of a predecessor to this movie, in a sense," says the Pennsylvania-born director.

Dream come true

"It was about two young boys and a girl in a British boarding school who had to fight a supernatural force."

But he adds that he would not send his own four children, aged between four and 12, to boarding school. "I'd miss them too much."

They are, however, going to school in England while the director completes the second Harry Potter film on which shooting has already begun.

Although Columbus does not yet know how many Harry Potter films there will be, he says he would love to make all seven - assuming JK Rowling publishes the expected final three books of the series - and he could easily imagine living in London for several more years.

Home Alone: Another US blockbuster

Getting the opportunity to direct films in Britain was a dream come true, says Columbus, admitting to being "a bit of an Anglophile".

"I was obsessed with British cinema from when I started out as a film student. I always liked the early David Lean films and the Ealing comedies as well as British humour.

"Monty Python and all those things were a part of me when I was growing up."

For a director better known for such American favourites as Home Alone and Mrs Doubtfire, getting the UK flavour of Harry Potter right was crucial.

Tips

"The Britishness of the film was something I was committed to from the beginning," he says.

The author of the Harry Potter books, JK Rowling had insisted on an all-UK cast and was determined that the film should be a faithful reflection of her creation.

Columbus says he was delighted to be able to consult her on the detail of the world she had imagined, getting tips on casting and costumes.

JK Rowling is currently writing the fifth Harry Potter instalment

He does admit to being nervous, however, when Rowling finally saw the film - he skipped the screening in favour of playing football with his children, and was relieved when he later got a call to say she had loved it.

While working on what promises to be one of the most popular films ever made in Britain, Columbus immersed himself thoroughly in UK life.

He goes to the theatre in London whenever he can, often reads five UK newspapers in a day and drives a UK car.

"I bought a Mini Cooper when I got here. I'm a big fan of the movie The Italian Job, so I've been driving it around the city."

'Dedicated'

He and his family are even going to spend Christmas in London this year, instead of returning home to San Francisco.

The experience of working with UK children has been a positive one too, the director says.

"British kids are so polite and they are just amazing actors - absolutely dedicated."

He believes they benefit from having role models such as Maggie Smith - who plays Professor McGonagall in Harry Potter - and Alan Rickman - who plays Professor Snape - because they are serious actors who constantly switch between theatre, film and television.

"Here (in Britain)," says Columbus, "it's all about becoming a better actor and maintaining consistency in your craft, as opposed to going from one movie to another and not trying anything different. I think that gets you kind of stale."