Four years ago Robert Pattinson's vignette in Vanity Fair hit the cutting room floor. Now he's set to become one of the actors of the decade, taking the lead in the phenomenally successful vampire love flick, Twilight, and playing Cedric Diggory in the upcoming Harry Potter. It's all happened so fast, he tells Donald Clarke

HERE IS a sad story. Four years ago, Robert Pattinson, then just 18, secured a role in Mira Nair's lavish adaptation of Vanity Fair. When the night came for the premiere, he slapped down his unruly hair, polished his shoes and stepped out proudly for Leicester Square.

"It was my first real job," he says with a wry smile. "I went along to the premiere, but nobody had told me that I had been cut out. I didn't realise until the film ended." Happily, the story has a jolly coda.

"The casting agent was the same one who did Harry Potter. They felt so bad about it they gave me an early meeting for the next Harry Potter film. And that went well." Indeed it did. As 2009 looms, 22-year-old Robert Pattinson finds himself teetering on the brink of full-blown stardom. That meeting with the Harry Potter people went so smoothly that he secured the role of Cedric Diggory - doomed rival of the hero at the Triwizard Tournament - in Harry Potter and the Goblet of Fire. The odd TV job and the occasional independent film followed. Then, early this year, he secured the role of Edward Cullen, teenage vampire, in the film version of Stephenie Meyer's hugely popular Twilight.

"I didn't even know there was a book series of that name," he says.

"This vampire love story thing? I had zero idea about it. It all came out of nowhere. Then they said the books had sold 25 million. I thought: 'is that a lot, 25 million worldwide?' I really didn't know."

It certainly is a lot. The Twilight books - four volumes so far - have generated a movement that strains definitions of the word "cult". Most likely, you either love Meyer's books, in which a sensitive teenager falls in with a cadre of morally upright vampires, or you have never heard of them. Unsurprisingly, Twilight fans have cornered a substantial sector of the internet for their own use. Every announcement from the studio was examined for evidence that the film-makers were daring to deviate from the sacred text.

Catherine Hardwicke, director of Thirteen and The Nativity Story, both films about teenage trauma, was signed up for megaphone duties. Kristen Stewart, rising star of Panic Room and What Just Happened, would play the sensitive heroine Bella Swan. There were rumblings at both announcements, but the news that some posh English bloke had secured the role of dishy, distant Edward unleashed a veritable tsunami of whingeing.

Was Robert unwise enough to pay attention? "I did a little bit and that was a bad idea. I won't make that mistake again," he says. "There was just universal disagreement with the decision. I suppose it was quite funny. That was my first real experience of Twilight mania. Seventy-five thousand people signed this petition saying the part should be recast. Seventy-five thousand! I do think it's funny now." When Meyers herself endorsed Pattinson, the temperature warmed somewhat.

"Whatever Stephenie says goes, I think," he says.

Most of the few wavering dissenters were won over when the film opened in the United States three weeks ago. A canny blend of gothic romance and loose-limbed naturalism, Twilight took in $7 million on midnight screenings alone. It went on to gather $70 million on its first weekend and secure the record for the biggest ever opening by a female director.

"I did Jay Leno the other day and he asked how it's been for the last few months," he says. "I had to say that it didn't explode until the previous five days. It was that fast. The other day I went in to buy a bagel in this place I normally go. There were four magazines with me on the cover. One said I was heading for a breakdown. Then I'm on Leno, looking at his iconic face. It is so weird."

Next Big Things come alone quite frequently. But I would be astonished if Robert Pattinson did not go on to become one of the most conspicuous film stars of the next decade. Fiendishly charismatic with narrow eyes and hair that obeys its own defiant rules, he combines the looks of an archetypal movie rebel with a striking intelligence that should, all being well, keep him out of the usual Hollywood catastrophes.

There were, he tells me, no actors "in his gene pool". Raised in London, the son of a businessman who imported vintage cars and a mother who worked for a modelling agency, Pattinson dabbled a little in drama as a teenager, but, when the time came to apply for university, still depressed by the Vanity Fair experience, he decided to study political science. Before he had time to fill out the form, however, he had secured the role in Harry Potter.

Pattinson walks through Twilight with the aspect of a man who is embarrassed by his own mighty power: he can fly, read minds and stop speeding motorcars. He adopts the same dazed look when considering the unusual position in which he now finds himself. He doesn't even know where he lives these days.

"I really can't answer that question," he says. "I get mail at three different addresses. I used to have a nice, tiny apartment in Soho and I miss not living out of a suitcase. But I wouldn't say I really want to put down roots either."

When Robert Pattinson was asked about his favourite films recently, he produced a list that included work by Bernard Rose and Jean-Luc Godard.

So, he's no fool. He must have some insights into the causes of the Twilight phenomenon. What's the series about? Burgeoning sexuality? The end of childhood? Some conservative critics have noted Edward's reluctance to become intimate with Bella - he's afraid he will chew on her flesh - and have decided the film is an argument for sexual abstinence.

"I don't know. That's hard to answer," he says. "Yeah. A lot of people point out that Stephenie's a Mormon and say the story must be about abstinence. I don't really think the film is about anything but itself. She didn't write the book for anybody else. She had a dream and wanted to write about the characters in that dream."

The story does seem to say something to teenage girls in particular.

"That's right. There is a clan mentality in young girls and that accelerated it. You go to a school and ask who's read the book and they all compete to say they have. That really drives success."

At any rate, the galloping popularity of the film version has ensured that adaptations of the other three books will follow. Pattinson looks set to have his life disrupted for some time to come. How will he manage to sustain friendships and romantic relationships?

"Well, I have been skipping off around the world for ages," he says. "And I have somehow managed to keep the same friends throughout all that time. We all do things where we are leaving home for ages. That's par for the course. But I never have much of a social life anyway."

It sounds as if he is ideally suited to the vampire lifestyle.

• Twilightopens next Friday