WHAT’S your favourite Roald Dahl book? For Elliot Harper, who plays sadistic headmistress Miss Trunchbull in Matilda the Musical - heading to the Alhambra for a month-long run - it’s The Enormous Crocodile.

His other top Dahl books are:

* James and the Giant Peach

* Charlie and the Chocolate Factory

* Matilda

* The BFG.

Agatha Trunchbull - one of Dahl’s most memorable characters - is a “dream role” for Elliot. When it comes to scaring children senseless, Miss Trunchbull is up there with the Child Catcher.

The champion shot putter and formidable headmistress of Crunchem Hall School is a sadist, a bully, a tyrannical monster who frightens the life out of pupils and teachers. She carries a crop and isn’t afraid to use it. She forces a boy to eat a huge chocolate cake, as punishment for taking a slice. She swings little girls around by their pigtails, throwing them high into the air like ragdolls. And you don’t want to know what she did to swipe the inheritance of sweet-natured schoolteacher Miss Honey, left timid and fearful from a childhood of slavery at Trunchbull’s hands.

Does Miss Trunchbull have any redeeming features? “No, I don’t think she does,” laughs Elliot. “But as an actor, you have to understand where your character came from, how they are what they are. Trunchbull was bullied when she was young, and that can turn someone into a bully. She plays by the rules and uses rules to control and dominate. This comes from her days as an Olympic athlete; she was the 1969 UK hammer-throwing champion then, at the Munich Olympics, she stepped outside the circle which led her to fail. In her Hammer Song she sings about how life is all about saying inside the line. It’s when she loses control, thanks to Matilda, that Trunchbull finally goes mad.”

Matilda is the much-loved story of a clever little girl with extraordinary powers who loves books, but is cruelly dismissed by her philistine parents and oppressed by her sadistic headmistress. When Dahl’s 1988 book was commissioned by the Royal Shakespeare Company, adapted by writer Dennis Kelly, with music and lyrics by Tim Minchin, it cleaned up at the 2012 Olivier Awards and became a global hit. The “anarchically joyous, gleefully nasty and ingenious” adaptation captures Dahl’s delicious darkness, with new touches including a poignant back story for Miss Honey.

“It’s a genius interpretation,” says Elliot, whose theatre credits include One Man Two Guvnors and Les Misérables in the West End and touring productions of Jesus Christ Superstar and The Buddy Holly Story.

“The music brings so much to story’s darkness and irreverence. It’s a family show but it’s not a light and fluffy musical. Tim Minchin is a bit mad but a lovely guy, his songs are quick and detailed - quite a vocal challenge.”

It’s a very physical role too, with Miss Trunchbull leaping around the stage, and chucking children into the air.

“She’s always played by a man, I guess that’s to do with the visual and physical requirements - you have to be strong and tall for this role. I’m 6ft 2,” says Elliot. “When I was researching the part an archivist at the Roald Dahl Museum who sent me a description of the original Miss Trunchbull. She always had a gin and a cigarette on the go, and was truly grotesque.

“It was initially quite daunting to play her, I’m still pinching myself. There’s an expectation that comes with this character, but you want to put your own stamp on it too. Hopefully I have. It’s about a girl taking control, which is relevant for these times. Matilda stands up to bullies and creates her own destiny. There’s also a theory that she shares some of Miss Trunchbull’s characteristics. She’s stubborn and hard-nosed, with a similar determination.”

Thankfully, unlike the tyrannical shot-putter, Matilda steps outside the line...

* Matilda the Musical is at the Alhambra, February 19 to March 23. Call (01274) 432000.