"It's the final battle," explains producer David Heyman. "Voldemort has called a truce to give the school the opportunity to turn Harry over to him. Harry, Ron and Hermione come back into the great hall and witness lots of dead bodies. It's a very sobering moment."

Rupert Grint's Ron Weasley stands in middle of the destruction and breaks down in tears as he discovers his friends have been killed in the latest skirmish. Emma Watson's Hermione consoles him as Hogwarts' staff hurry around them tending to the endless wounded. Harry stands there bloodied and agonised.

"Part One is quite an interesting film about these kids dealing with the real world," continues Yates. "When you get kicked out of Hogwarts, you're in a very dangerous place and you need to grow up fast. And Part Two is a big action picture, basically, which has a very emotional resolution."

"It's a lot more grown-up than anything we've done so far," says Yates. "This one is particularly violent at times so it'll be quite interesting when we present it to the studio."

True enough, Radcliffe looks like he's in the wars. "These are wounds that happen to me from various things in the battle," he tells. "In the last two hours of the film, I start becoming a bloody mess. The action in this film is going to be pretty extraordinary."

Radcliffe gets up to leave, still looking like he's been hit by a truck. "Sometimes I leave the set with this on," he says, examining his colourful wounds with a grin. "It makes me look tough."