LONDON - Some actors might balk at being cast as an evil witch. Not Helena Bonham Carter.

The British star revels in the role of sadistic sorceress Bellatrix Lestrange -- fanatical follower of evil Lord Voldemort-in "Harry Potter and the Order of the Phoenix,'' the fifth film adapted from J.K. Rowling's wizarding saga.

Vivid proof that there are no small parts in the hands of a larger-than-life performer, Bonham Carter blazes her way across the screen in her one big scene-a dramatic battle between Voldemort's Death Eaters and Harry's ragtag band of friends.

"I had about five lines and I think they cut about three of them,'' Bonham Carter, 41, said in an interview before the film's release this week. "So I knew I had to be conspicuous.''

Conspicuous is an understatement. Black-clad, wild-haired and cacklingly sadistic, Bellatrix escapes from Azkaban prison to join the resurgent Voldemort in his quest to destroy Harry and control the magical world.

Bonham Carter says she had a big say in creating the character's voluptuous-but-disheveled look.

"At first they thought, `Oh, we'll just put her in a sack,' '' Bonham Carter said. "But I said, `There's no way I'm going to wear a sack. I've got to be a sexy witch.'

"I wanted a sort of bodice thing to give me a shape. There is a bit of the warrior about her-Bellatrix means warrior. She's the right-hand Death Eater to Voldemort.

"I also wanted everything to be splitting at the seams and a bit of `Sunset Boulevard' disintegration to be going on, because she's been in prison for so long. She has a very posh, aristocratic carriage, because she's pureblooded, but at the same time she's completely divorced from reality.''

Over the five films, the Potter series has become a showcase for some of Britain's finest actors-Bonham Carter jokes it is "like a rest home for British Equity.''

Her "Order of the Phoenix'' co-stars read like a roll-call of thespian talent: Ralph Fiennes as Voldemort, Michael Gambon as Hogwarts' headmaster Albus Dumbledore, Alan Rickman as the sinister Severus Snape, Imelda Staunton as bossy teacher Dolores Umbridge and Gary Oldman as Harry's godfather, Sirius Black.

"I spent most of the time in my trailer reading and chatting,'' she said. "It was like my Harry Potter holiday.''

She also enjoyed working with Daniel Radcliffe, who plays Harry, and the other young actors-particularly Matthew Lewis, who plays Hogwarts student Neville Longbottom. A previously meek pupil whose parents were tortured to insanity by Bellatrix years earlier, Neville comes into his own in a confrontation with his nemesis.

Bonham Carter said she took her character's sadistic streak "a bit too literally'' during the fight scene, accidentally inserting her wand into Lewis' ear.

"I sort of bruised his ear inside,'' she said. "He had to see a doctor; there was slight internal bleeding. I was mortified.''

Bonham Carter gained fame in the 1980s in the Merchant-Ivory costume dramas "A Room with a View'' and "Howards End,'' and has worked ever since to shed any hint of period-piece typecasting. Her eclectic list of credits includes 1997's Henry James adaptation "The Wings of the Dove,'' for which she received a best actress Oscar nomination, 1999's "Fight Club'' and 2005's "Charlie and the Chocolate Factory,'' directed by her partner, Tim Burton.

She's just finished shooting, opposite Johnny Depp, on "Sweeney Todd,'' Burton's musical about the legendary "demon barber of Fleet Street.'' Bonham Carter had to learn to sing for the role of Mrs. Lovett, baker of macabre meat pies-she says it was "fantastic, probably the most fulfilling thing I've done for ages.''

Like millions of Harry Potter fans, Bonham Carter is awaiting the July 21 publication of Rowling's final Potter novel, "Harry Potter and the Deathly Hallows,'' to learn the characters' fate. But she has been given a hint that Bellatrix may play a part.

While she was considering whether to except the relatively small role in "Order of the Phoenix,'' she says, "J.K. Rowling sent a message saying she's going to be very significant in the last one.''

Make of that what you will, Muggles.

"Harry Potter and the Order of the Phoenix'' opens around the world from Wednesday.