6 December 2011 Last updated at 22:29 ET

Bertie Carvel plays Miss Trunchbull in Matilda The Musical

By Tim Masters Entertainment and arts correspondent, BBC News

Bertie Carvel is reprising the role he created for the RSC's Stratford production

As he makes his West End debut in Matilda The Musical, actor Bertie Carvel explains why his child-tossing tyrant Miss Trunchbull is much more than a pantomime dame.

She is one of the most grotesque characters in the Roald Dahl universe.

Agatha Trunchbull, the headmistress of Crunchem Hall Primary School, likes to toss little girls by their pigtails and punishes her pupils in a torture device known as the Chokey.

In Danny DeVito's 1996 movie version, Miss Trunchbull was played by Pam Ferris.

But the RSC production of Matilda The Musical gives the role to a man - Bertie Carvel.

Bertie Carvel is nominated in the Whatsonstage.com awards

The 34-year-old actor has received ecstatic reviews for his portrayal of the large-bosomed battle-axe in Stratford-Upon-Avon and now at London's Cambridge Theatre.

"This woman is a psychopath, a murderer, a child abuser," says Carvel when we meet at the Whatsonstage.com awards launch party.

We are huddled at a table surrounded by 600 actors, directors, designers, playwrights and producers getting in the Christmas spirit.

"She's not without sympathy of course," he says above the noise, "because one has to discover as an actor the reasons why someone would act in such a way.

"She's got all kinds of complications to her psychology. She's a pretty filthy human being, yet we of sort of love those characters."

Chilling voice

Carvel's Miss Trunchbull first appears on stage like a classic Bond villain: sat in a high-backed chair scanning a tower of flickering TV monitors.

Then there's her crooked hand, the slight hunch and a chilling voice that's been compared to Hannibal Lecter. So where did that come from?

"It's a composite of different things," says Carvel.

"I work out where she was born and when, and what kind of education she would have had. It's also about channelling a melange of people one has known - but I'm pleased to say I never had teachers like Agatha Trunchbull."

Miss Trunchbull puts her "maggots" through their paces

Although this is Carvel's first West End appearance, he has been busy in theatre, TV and radio since graduating from Rada in 2003.

His theatre work includes Doctor Dee (Manchester International Festival), Rope (Almeida), The Pride (Royal Court), and The Man of Mode, The Life of Galileo and Coram Boy (National Theatre).

His first musical was 2007's Parade at the Donmar Warehouse, which earned him an Olivier award nomination. His TV work includes Hidden, The Crimson Petal and the White, Sherlock, John Adams and Doctor Who.

But it is Miss Trunchbull that will be keeping Carvel busy until at least mid-April.

It's tempting to think of her as a pantomime dame, but Carvel argues she's more complex than that.

"It's redolent of the pantomime, but it would be hugely limiting to approach the character that way," he says. "The thing about the pantomime dame is there is a certain kind of tongue-in-cheekness that the actor is sending up the fact they are cross-dressing, and that is not what I'm trying to do at all."

He's delighted by anecdotal evidence that some still did not know there is a man underneath the wig and the padded costume.

"As with any character you play you want people to believe you are who you say you are, even though everyone in the room knows that it's a lie.

"I love the challenge of asking people to believe that when you are a 34-year-old man playing a 78-year-old woman.

"I jump up and down in glee when people in the audience tell me the person in front of them didn't realise it was a man!"

Carvel admits that during the Stratford production he tried to stay in character backstage, but he's been harder to sustain over time.

"A funny thing has happened recently," he laughs.

Matilda the Musical arrives in London after a well-received run in Stratford-Upon-Avon

"I find Miss Trunchbull is hovering there always, so I can be having a conversation with the lady who puts my wig on, and Agatha will chime in with a comment and this banter occurs between the three of us!"

Carvel has no plans beyond Matilda he can talk about, though he has played Mark Darcy opposite Sheridan Smith in a workshop for Bridget Jones' Diary: The Musical.

"I think there will be more workshops soon," he says. "I can't speculate, but work is continuing with a certain amount of excitement and a lot of anticipation from all quarters."

And did he read the five-star Matilda reviews?

"I have to confess to reading a few. Normally I avoid them, but I read them after we finished in Stratford so it seemed a bit weird to avoid them again. I've read one or two and they're very nice - so thank you very much!"