SHE may look like a stalwart of the Women's Institute, but Professor Dolores Umbridge is no jam and Jerusalem kind of woman.

ake her smile. Her requests, no matter how unfair or unreasonable, are always accompanied by a smile. A killer smile.

Not that Imelda Staunton, who plays this addition to the Harry Potter gallery of characters in the latest film taken from JK Rowlng's bestselling series, would necessarily view Umbridge as a villain.

She's sent to Hogwarts school for young wizards to shake things up and put an end to all the stories that the evil Lord Voldemort has returned to mess things up.

"She's just trying to do a very good job in a not very good way," suggests Staunton, Oscar-nominated for her performance in Mike Leigh's film, Vera Drake.

"I mean, she's following orders, but she realises what the Ministry of Magic is suggesting just isn't going to do the job. So she has to take things in her own hands and sort Hogwarts out, particularly Harry, and get things changed for the better."

Staunton says she finds such people terrifying because they have no objectivity. She's just following the path, completely blinkered in doing what she's doing. "And that is frightening, I imagine, to witness that," she says.

"But, regardless of what anyone thinks, she is just going to do what she has to do. No one really questions her. Well, Harry does and that's terribly dangerous."

As you can tell, Staunton approached the role as seriously as any other. Vera Drake, dispensing tea and abortions in 1950s London, and Professor Dolores Umbridge, tyrant and oppressor of Harry Potter, are given equally serious thought.

She realised Umbridge could turn into a very broad performance but remained determined to make her as real as possible. "If you've got that veneer going that people believe in, then the underneath stuff that comes out later, hopefully, is more shocking," she says.

"The smile and the grin and the laugh are part of her make-up, the way she dresses, the way her hair is - it's all to present a pleasing picture and, therefore, nothing in her world and the other people's world can be wrong."

The smile - more of a fixed grin like a politician trying to look sincere - is part and parcel of her character. "I don't think she's a natural smiler because they're not genuine smiles. You know she certainly isn't at ease with herself but, my God, she's worked hard at creating a picture and creating a front," explains Staunton.

"I just experimented with things that felt right. I didn't practise in the mirror or anything like that. That's where the challenge was with this part, because I thought she'd sort of smile and grin, but there's no point doing that unless there's this bubbling volcano underneath."

The importance of costume in the Harry Potter films is explored in the ITV show, Harry Potter: The Costume Drama, tonight and Dolores Umbridge's look is certainly distinctive. She's not so much pretty in pink as pretty awful in pink. Not only her clothes but her room is a riot of pink. "Well, some people power dress, don't they? The more power she felt she was gaining, the more confident her colours became," says the actress.

"She thinks Hogwarts is in complete chaos. She doesn't want that, she just wants everything clean and neat and nice and hopefully pink, I daresay. But she does it to herself and gives herself that status with those colours."

Staunton had fun playing Harry's tormentor, not least being in the Great Hall addressing Hogwarts pupils. "I loved that with her WI hat on and her handbag, you know, a bit Thatcher," she says. "It was glorious doing that. If you listen to what she's saying, it's the Nazis combined with complete control."

Despite the mention of Thatcher, she says she didn't have anyone in mind when creating Umbridge. "I've only started thinking about that now, because at the time I didn't talk about it's like this and like that. She's that person, she's not like anyone else, she's this creation," she says. "But I did think of the WI, just the way she looked."

The film also reunites her with Daniel Radcliffe, the screen's Harry Potter. She's known him since he was ten and they appeared together in a BBC-TV adaptation of David Copperfield.

She thinks he's fantastic. "The scenes we had together, I loved them. I'm very serious and concentrated about my work and he is," she says.

*Harry Potter: The Costume Drama, a rummage through the wizard's wardrobe, is on ITV1 tonight at 6.10pm and a T4 Movie Special reporting from the premiere is on C4 at 1.25pm today.

Harry Potter And The Order Of The Phoenix (12A) is now showing in cinemas.