"I never play down to the audience," says Mark Peachey.

"I mean, essentially I'm a grown man running around in an 8ft suit pretending to be a monster but I take it very seriously. In my head, when I go on stage, I am The Gruffalo."

Considering that The Gruffalo is an imaginary creature with "terrible tusks and terrible claws and terrible teeth in his terrible jaws", this act of professional empathy must take quite some effort. But Peachey is right to take his task seriously.

The Gruffalo is also a marketing phenomenon - the Harry Potter of the picture book world which, since 1989, has won the Smarties Gold Award, been translated into 26 languages and made its creators, author Julia Donaldson and illustrator Axel Scheffler, the most successful duo since Allan and Janet Ahlberg.

A monster who is both scary and cuddly and whose rhyming speech acts on children like a drug, The Gruffalo is a worthy successor to Maurice Sendak's perpetually enthralling Wild Things.

And, anxious that he shouldn't be turned into "something sickly", his creators have rejected offers to turn their book into a film.

They would have been unwise, however, to say no to Tall Stories, a non-profit-making theatre company which has gained international acclaim for its innovative storytelling.

Committed to the language and atmosphere of the book but with plenty of witty songs along the way, its three-person adaptation won blanket praise when it first toured in 2001 and is now back on the road before hitting the West End.

Peachey is the seventh actor to take on the role (the phrase "Gruffaloed out" could soon enter the theatrical lexicon) and he likes to think he's brought something new to the part.

"I've heard of one Gruffalo who was as shy as anything," he says, "but when I enter I try to scare the living daylights out of them. I roar, I jump up and down and I tell them I'm going to eat them.

With the three-year-olds it's like you're seeing fear in their eyes for the first time. "But he's not scary really," he reassures us. "There's a bit in one of the songs about how he'd like to learn how to hula, travel the world and draw works of art. I must be doing something right because the cuddly toys are selling like hot cakes."

For those unfamiliar with the story (and, judging by the number of kids Peachey has overheard anticipating his lines, you're very much in the minority), The Gruffalo is the tale of Mouse, a diminutive trickster who heads into the deep, dark wood on a hunt for hazelnuts.

Encountering a series of potential predators - the wheeler dealer Fox, the retired RAF Owl and the maracashaking party animal Snake - he scares them away with stories of an imaginary monster friend, The Gruffalo.

But what if Mouse's fantastical invention were actually to exist? Well, it sure proved a task for the wardrobe department. But while the kids seem happy with their efforts, the same can't be said for Peachey's fellow cast members.

"My costume is very hot and heavy," he explains, "and it can sit in a bag for three days in between venues. Sometimes Mouse will say to me, 'Ooh, you smell a bit today Gruffalo'. At the moment we're using Febreze."

Starts 10.30am every day plus 1.30pm on Weds and Fri and 12.30pm on Sat. Tickets cost £9.50/£8, call 08700 606 650.