JK Rowling is his consigliere, Richard Harris was his noisy guest, Daniel Radcliffe is his protege. David Heyman, producer of the Harry Potter films, tells Michael Dwyerabout bringing the series - and the latest instalment, Harry Potter and the Order of the Phoenix - to the cinemas

ASCENDING the winding staircase of Claridge's, it appears that the first floor of the London hotel has been turned into a Harry Potter theme park.

At the top of the stairs stands a tailor's dummy dressed in the pink costume Imelda Staunton wears as malevolent Professor Dolores Umbridge in Harry Potter and the Order of the Phoenix. Down the corridor, a wall is covered in plates adorned with photographs of cats, although they do not move and squeak like the cats on Umbridge's plates in the movie.

The hotel is swarming with journalists from across the world in the build-up towards next week's international release of the fifth film in the phenomenally successful franchise - the first four have amassed more than $3.5 billion. This is followed on July 21st by the publication of Harry Potter and the Deathly Hallows, JK Rowling's concluding book in the series.

While Rowling is the force behind the books, David Heyman is the producer behind all the movies.

"I loved the first book," says the 45-year-old Londoner as we settle down to talk. "I found it compulsive reading and I finished it in one sitting. I had no idea the film would become as popular as it did. I thought that if I were lucky, it would do as well as Chitty Chitty Bang Bang or The Railway Children. I don't think anyone even hoped it would do so well, that it would make $970 million."

That first film, Harry Potter and the Philosopher's Stone (2001), came together surprisingly quickly, Heyman says. "Warner Bros optioned the first book for me. I think they gave it to me because I had gone to an English public school, and I could understand that aspect of it. I read the book at the beginning of 1997 and they had closed the deal before the end of that year. Good fortune fell on me because the book became a huge hit around the world."

Given that Rowling is famously attentive to every detail of her publishing arrangements, did Heyman ever feel she was looking over his shoulder as the films were prepared?

"Not at all. Jo is not looking over my shoulder, but she is there as a consigliere when needed. On this film, for example, there was a character we were considering cutting. I always send her an early draft of the script, and when she read this one, she pointed out that this character was missing. She said that we may end up putting ourselves in pretzels to get that character into the seventh film because the character features again in the final book. Of course, I had not read that book, so we took her advice and put that character back in."

The new film, he notes, features various family members of Harry Potter's godfather, Sirius Black (Gary Oldman). "I called Jo and told her we were working on visualising them. I asked if she could give us some more information on the Black family tree. Within 15 minutes she had sent us a fax going back through six generations of the Blacks, with about 100 names, birthdays, death dates, and who married whom and how names were pronounced. The detail was remarkable."

Rowling also came to their assistance on filming the ending. "It's a very internal ending in the book and we were trying to externalise it. Jo was incredibly helpful and came in to discuss that, but only because we asked her. She has a wonderful imagination. Children's films are so often puerile and condescending. I am proud of the Potter films because they are real films. They are mature and respect the audience."

The son of film producers John and Norma Heyman, the producer of the Harry Potter series grew up steeped in a world of movies. When David was 10 he acted in one of his father's productions, Bloomfield (1971), directed by and starring Richard Harris. Decades later he would work with Harris again, when the late actor played Hogwarts headmaster Albus Dumbledore in the first two Potter movies.

"I was a terrible actor," Heyman says. "I'm not so sure either about Richard Harris as a director, although he was better as a director than I was as an actor. He was like my godfather. My father was his agent in the 1960s and he lived with us for periods of time. He was quite a noisy guest, but a lovely man, and greatly missed. They don't make them like that anymore."

It must have seemed entirely natural, I suggest, for Heyman to follow his parents into producing movies.

"I would be lying if I said I went into producing because it was something I had to do. I just love film. I love going to the cinema and enjoying the experience of watching a big wide screen filled with images, and being transported into another world. I began working in films as a summer job, as a runner, and fell in love with the business. Well, actually, I never fell in love with the business but with the process of making films and working with writers and directors and actors and crew. Getting the financing together is something I find less pleasurable."

What was the best advice his parents gave him? "To have passion. You've got to believe in what you are doing. You have to have that in spades because you are faced with challenges every step of the way. People will tell you 'no' over and over again. You have to be prepared for a long journey every time.

"My parents were a great inspiration to me, in the way they would always strive for very high standards, and in their fundamental decency, which I hope I live up to. They raised me to be honest and to have respect for other people."

I mention that those are not characteristics associated with quite a few producers.

"I know," Heyman says, "but I think it's vital. The films I am interested in making have humanity in them. That's another reason I'm proud of this film. It's the most emotional of the Harry Potter films, and the most humane of them, and the most complex psychologically. It's about a boy who is isolated and alone. Harry feels as though nobody understands him and nobody cares. Then he becomes embraced by his friends and the power of their loyalty and devotion to him, and he becomes a teacher and a leader."

The film features the first screen kiss for Harry Potter, played by Daniel Radcliffe, as he stands under magically conjured mistletoe with fellow student Cho Chang (Katie Leung). "I've known Daniel since he was 10 and seen him grow up before my eyes," Heyman says. "Then, here we were watching him have his first screen kiss. I kept thinking that I shouldn't be watching, but it was perfect, a tender and beautiful moment for audiences."

Shortly after the new film finished shooting late last year, Radcliffe made headlines when, at the age of 17, he took the leading role in the London stage revival of Equus, which required him to be naked in several scenes. Was Heyman worried that this would be detrimental to the actor's image with three more Harry Potter pictures yet to come?

"I was concerned only in the sense that I wanted him to do his best in the play," says Heyman. "I didn't want him to fall on his face. I had complete confidence in him. He's a really fine actor and an ambitious young man. He is determined to push himself to be great in whatever he does. He is shockingly bright. He reads voraciously. He's also very thoughtful, so the decision to do Equus was not something taken casually."

Heyman sounds paternalistic as he talks about Radcliffe and his young co-stars in the series, Rupert Grint and Emma Watson. "I want everything for these kids. I want them to pursue their craft and be the very best that they can be. I think Daniel is that boy. I think it would be foolish not to encourage him to seek out other opportunities where he can push himself. In fact, I believe that his performance in this film fed his performance in Equus, and his performance in Equus will feed his performance in the sixth film. Each of those experiences has made him an even better actor."

Harry Potter and the Order of the Phoenix opens next Thursday

Luna Lovegood from Louth

Harry Potter and the Order of the Phoenix introduces a striking newcomer to the series in Evanna Lynch, who turns 16 next month and is from Termonfeckin, Co Louth. She brings a dreamy, ethereal quality to the role of student Luna Lovegood.

"We had this open casting call in London and over 15,000 people turned up," says producer David Heyman. "Some of them were obviously not suitable. There were 40-year-old women and people over six foot four. It was bizarre, but our casting director saw all of them and narrowed them down to 260, who were put on film. Of them, about 30 were shown to us."

Heyman, fellow producer David Barron and director David Yates watched the tapes separately, and each made the same choice.

"The other girls could play Luna, but we knew Evanna could be Luna. Evanna is Luna. She creates her own universe. She's very bright and confident, and she told us if we didn't cast her, it was our problem. She didn't say that in an arrogant way. She just had self-belief and knew she was right for it. She's an obsessive Harry Potter fan. She even made her own earrings for the film. She had been corresponding with Jo Rowling for years.

"When I called up Jo and told her we had cast Evanna, Jo was gobsmacked."