DANIEL Radcliffe drips his way into the white marquee, his T-shirt, jeans and hair soaking wet. As he sits down, a small puddle of water forming around his feet, he begins to inspect his blackened fingernails, before directing his gaze at me.
• Radcliffe, Watson and Grint at last week's premiere of Harry Potter And The Deathly Hallows: Part 1 Picture: Getty
Following behind the 21-year-old are co-stars Emma Watson, dressed in the typical garb of alter ego Hermione Granger - an ill-fitting purple hoodie and dirty grey jeans - and Rupert Grint channelling his character Ron Weasley in a baggy T-shirt and jeans.
The trio are at Leavesden Studios, just outside Watford, where the seventh and final chapter of the Harry Potter franchise, Harry Potter And The Deathly Hallows, is being filmed. And by the looks of it, they're being put through their paces.
The gang have just finished filming a pulse-pounding foot chase, as they tried to outrun a gang of Voldemort's Snatchers, and this has clearly unleashed some healthy rivalry between the stars.
"I do a hell of a lot of running in this film, and I'm achy and stiff," admits Watson, 20, collapsing into her chair. "I've pulled a lot of muscles, but it's good fun. I definitely gave the boys a run for their money!"
Grint, 22, adds: "It got quite intense, especially since we were having to dodge between trees and jump over logs. I don't exercise so it was quite hard."
Radcliffe interrupts: "All those years of training with the stunt team finally paid off. There was no question in my mind that I could beat them, not that I'm competitive or anything!"
The David Yates directed film, based on JK Rowling's bestseller, is split into two parts. Harry Potter And The Deathly Hallows: Part 1, is released tooday while the finale, which will also be shown in 3D, will be out in July 2011.
"It's frustrating for fans," admits Radcliffe. "But not everyone is willing to sit through a six-hour film. This was the only way we could tell JK Rowling's story in a complete and fulfilling way."
The story picks up where Harry Potter And The Half-Blood Prince left off, with Harry's arch-enemy Voldemort (Ralph Fiennes) continuing his mission to kill the boy wizard, who has now left the comfort zone of Hogwarts School with his two friends.
"Right until the end, we're not in Hogwarts at all. It makes a huge difference and gives the film a really different feel," Radcliffe continues.
Filming has taken place around England, Scotland and Wales, as well as at Leavesden and Pinewood studios.
"It's nice to be out of the studio. It's such an emotionally heavy film, it's good to do something more physical," says Watson, who has taken a break from her studies at Brown University in the US to focus on filming.
But being away from the safety of school is clearly making the trio more vulnerable to Voldemort and his dark ways, as their final scene demonstrates.
Friction is also building up between the two teenage boys, as Ron gets paranoid about Hermione and Harry becoming closer.
"It's a different Ron to the one we're more familiar with. He erupts and shows his dark side," says Grint.
Radcliffe nodds vigorously, adding: "Both Harry and Ron are in the wrong and they know it, but in a very male way. When you've waded too deep to get out, it escalates and the situation severs their friendship briefly."
Having left school, the boys are now free to follow their hearts, without fear of detention, and that leads to some racy scenes.
"People wonder what would happen if Harry and Hermione got together and they get to see that happening. It's quite funny," Radcliffe reveals. "I'm covered head to toe in silver body glitter!"
The Harry Potter phenomenon, which began ten years ago, has turned the trio from unknown child actors into multi-millionaires, propelling them to Hollywood fame - and yet, they appear as grounded and down-to-earth as they must have been when they first began filming.
"I've got to give credit to my parents and the people on set, because if I'm acting like an idiot, they'll tell me," says Radcliffe.
"In America, people have told me actors are treated like superior beings. I know some of them, and you wouldn't trust them to sit the right way around on toilets! We're as flawed and as idiotic (as anyone else], and nobody should place us on any kind of pedestals."
Their fortunes may allow them to enjoy early retirement, but the three actors have no plans to rest easy: "I still have ambitions as an actress. There's definitely more to see," assures Watson.
"I love working and I have no plans to stop," agrees Grint.
Radcliffe, who has enjoyed theatre stints in the West End and on Broadway in Equus, adds: "I feel like I have to work more than other people my age because it's partly about proving a point.
"If I, after doing this massive series of films and starting so young, can forge a career for myself through a lot of hard work and enthusiasm, then I pave the way for future generations of child actors.
"Having money gives you room to manoeuvre. I don't have to do a job for money. At the moment, I can be selective, based on my own passion and enthusiasm."
With the end nigh for Harry Potter, plenty of tears will be shed as they wave goodbye to their alter egos.
"I'll miss the relationships I have with the crew and that feeling of family," says Radcliffe. "I'll also miss playing the character. There are very few characters like this. It's very cool to play a hero and I may not have that again."
Watson, however, refuses to believe it, saying: "I'm in denial. We've got til next summer."
And Grint adds: "It's daunting and scary because we've been contained in the Harry Potter bubble. But I can't wait to change my hair colour!"
Radcliffe quips: "Being in Harry Potter is a lot like being in the Mafia, in that once you're in, you're never really out. We are inextricably linked to each other for the rest of our lives."