Harry Potter has done a lot of growing up since his film debut. Keiron Pim reports on hormones now raging at Hogwarts.

A generation of young readers has grown up with JK Rowling's Harry Potter books, not least the child actors who star in the wildly-successful movie series.

When the first cinematic instalment, The Philosopher's Stone, was released in 2001 Harry and his friends Ron and Hermione were fresh-faced 11-year-olds.

Four years later they are full-blown teenagers competing with raging hormones, the onset of acne - oh, and the odd fire-breathing dragon for good measure.

Rowling has penned six books to date, four of which have now been translated into films, and the latest reaches cinema screens nationwide on Friday, November 18.

Harry Potter and the Goblet of Fire is widely considered the best Potter book, with an epic story that sees Harry combating the growing presence of the evil Voldemort, fending off murderous mermaids in a wizardry competition, and also dealing with his own burgeoning feelings for the opposite sex. The book comes to 645 pages, which presented director Mike Newell with a headache - how to squeeze it into a movie that won't have kids fidgeting and getting bored?

“It's very daunting to start with. The book's as big as a house brick and I was very unsure quite how one would attack it,” he said.

“After a bit I think the thing itself just overwhelms you and what you do is you try to get from day to day and at the end of the day, looking back, I'm terribly proud of it.

“David [Heyman, the producer] was very clear to me when we first started to talk about me making the film that if I could see a way of making it in one film, then we could continue to talk. If not, then we should part friends - and there was a time when people were thinking about making two films.

“I read the book very carefully and I felt that there was a way of making one film, which means that there was a way of shedding the things that needed to be shed because the book is too big to be made as a single film.”

This meant focusing on key themes, such as the fact that Voldemort, played by an almost unrecognisable Ralph Fiennes, dictates the course of events from afar, only appearing on screen at the beginning and end of the film.

“Only little by little did Harry catch up with what was happening to him until it was too late, and there he was, facing the devil in a graveyard,” said Newell.

“As soon as I could see that, I felt that I could stay true to the book and keep the length down.”

If you don't know the story already, it goes like this: the Triwizard Tournament has come to Hogwarts School of Witchcraft and Wizardry. It is a centennial magical sports day involving competing wizard schools and Harry finds himself as Hogwarts' sole representative - despite not having put himself forward and being below the age limit.

He is up against two other young magicians, facing frightening challenges such as tackling the aforementioned dragons, spending an hour underwater eluding mermaids that try to drown them and finding their way through a dark maze that seems to have a life of its own. And always in the background is Voldemort, who finally presents himself in a terrifying showdown in a graveyard.

It's the first Potter film to carry a 12A certificate, which means that children under 12 may only watch it accompanied by an adult. Even members of the cast said they found parts of it scary to watch.

Emma Watson, who plays Hermione Granger, said: “I think to some extent our audience who were first fans of Harry Potter are growing up with the films, so that works out okay. Yes, to some extent we might have lost some of the much younger audience - I'm in it and I was scared - but at the same time I think that we will have gained from it.

“I think this one is much more of a thriller than it ever has been before.

“I love the fact that they haven't pulled the punches, I love the fact that they have gone with it and that they've made something which is true to the book.”

Newell, Heyman and half a dozen actors were speaking at a press conference in the suitably Potterish setting of the Merchant Tailors' Hall in the City of London's Threadneedle Street. They sat behind a trestle table on throne-like seats - Daniel Radcliffe, who plays the young wizard, sitting centrally on the largest chair - sipping their water from goblets. Behind them hung a row of six oil paintings depicting luxuriantly robed grand old men with eccentric facial hair, all with their eyes closed. A rich red tapestry decorated with birds and fruits and lions and unicorns formed a backdrop, and vast chandeliers were suspended overhead. You could imagine you were in the great hall at Hogwarts, were it not for the 300 or so journalists who had assembled to quiz the young stars.

On arrival at the reception desk, I had been asked my nationality and must have looked quizzical as I replied. “We have people from 87 countries here today,” explained the woman from Warner Bros.

A new Harry Potter film is seriously big business - the new film is likely to boost worldwide takings from the series to more than $3bn - but this doesn't appear to have turned the heads of its teenage cast. Radcliffe, now 16, comes across as thoroughly grounded and down to earth. The fact that he, Emma Watson and Rupert Grint (Ron Weasley) have done their growing-up on screen doesn't appear to faze him.

“It's been an odd five years but it's been great. We've got a while before the films end and we're not all absolutely confirmed as doing them all,” he said.

“We're all definitely doing the fifth but after that who knows? In a way [growing up with Harry] makes it easier to act in each of the films because, firstly, I've been through all the stuff that he's going through, like the hormones relatively recently, so it's quite fresh in my mind.

“And I suppose it's been made easier by the fact I've been doing it since I was 11. You get to know the character so well that it makes it easier to act in the long run.”

Watson addsd: “It feels like I don't really have to act any more.

“I'm so close to her and know her so well and there's so much of me in her and her in me that it feels like I'm barely doing anything sometimes!”

In the near future, however, they will all be looking to spread their wings and escape being typecast as the characters with which they have become so closely identified - Radcliffe will appear in a film set in a Catholic orphanage in the Australian outback, and Grint, who has already starred in Thunderpants, has completed a movie called Driving Lessons.

Radcliffe says: “The new film is centred on four young Australian boys who have grown up in a Catholic orphanage in the outback. The orphanage comes into some money via a donor and for their birthdays they send the boys to the sea for a couple of weeks, and it's just about the time they spend there.

“And so I think we're all looking forward to going on to other things.”

THE STORY SO FAR

t Harry Potter and the Philosopher's Stone (2001). Worldwide box office total: $968.6m (about £544m). Third highest-grossing film ever. An 11-year-old orphan discovers he's a wizard. During his first year at Hogwarts School of Witchcraft and Wizardry, Harry makes two friends (Ron and Hermione) and unmasks nervy Professor Quirrell as a traitor trying to return his master (Lord Voldemort) to power.

t Harry Potter and the Chamber of Secrets (2002). Box office: $866.3m (eighth highest-grossing film). Harry returns for his second year at Hogwarts to find the school gripped by panic. A dark chamber, created years before by muggle-hating Salazar Slytherin, has been prised open and Harry is number-one suspect. It's Ron's sister, however, who did the deed under the spell of Tom Riddle (16-year-old Voldemort).

t Harry Potter and the Prisoner of Azkaban (2004). Box office: $789.4m (15th highest-grossing film). In what JK Rowling says is her favourite film, besieged Harry (now 13) returns to Hogwarts, having learned that an escaped prisoner, Sirius Black, intends to kill him. With Ron and Hermione's help he flees Hogwarts and discovers the truth about Scabbers (aka Peter Pettigrew), who betrayed Harry's parents to Voldemort.

t Harry Potter and the Goblet of Fire (2005). Release nationwide November 18. During his fourth year at Hogwarts, the 14-year-old develops a crush on a student and finds himself chosen as an underage competitor in dangerous school events. New faces include Jarvis Cocker and two members of Radiohead as The Weird Sisters.