Despite frenetic Nu-Panto efforts to prove the contrary, it’s not playwrights, classical actors or an illustrious venue that make for a successful Christmas show. Nope, what festive entertainment really needs are funny, charming performers who treat the audience like a best friend. Step forward, Lisa Hammond, now playing an unconventional Beauty in the Lyric Hammersmith’s Beauty and the Beast.

As you’d quickly hear from fans of Told by an Idiot (creators of the show), or from the comedian Peter Kay (whose eye she caught when she worked with him), Hammond is one of the best and funniest actresses in the country. At 4ft tall she’s also one of the smallest. Not to mention the most stubborn. Her career has been dedicated to flouting expectations of the roles an actor of her size might play, and for her, Beaut yis a far more likely casting than, say, Snow White and the Seven Dwarfs.

Not that she denies her casting is unusual. “When I accepted the part,” she recalls, “I thought, ‘I’d love that challenge’. My second thought was, ‘oh God, are people going to buy it?’ ” Not only is Hammond small – her condition is a rare form of dwarfism called pseudo-achondroplasia – but she also experiences pain in her joints and so (often but not always) uses a wheelchair. The wheelchair has been incorporated into Beauty and the Beast as a prop that the whole cast use, “which makes the audience comfortable about it being on stage,” says Hammond. Her height, meanwhile, “is not acknowledged in any big way in the show. It’s just: that’s what I am. As long as we buy it 100%, audiences are willing to come along with that.”

And so they should be: from the mouthy, impish Hammond, they’ll get a more characterful Beauty than the usual drippy ingénue. Which is the Told by an Idiot way – these champions of offbeat theatre don’tdo orthodox. Hammond isn’t the show’s only unlikely performer: her father is played by a woman (Yolanda Vasquez), her ugly sisters by Hayley Carmichael and Nick Haverson, and her dog, by the wonderfully gormless Spanish performer Javier Marzán. “So it’s not just me sticking out like a big red light,” says Hammond. “Everything else is a bit crazy.”

So far, the worst she’s had to experience was the rowdy schoolchildren’s performance that preceded this interview. “Isn’t she beautiful?” one of her co-stars asked the audience. “No,” sniped back a snotty-nosed youth.But Hammond can laugh at that. “It excites me,” she says, “because it’s so honest. At least they are not going” – and she mimes a behind-the-hand whisper – ‘I think we should think she’s beautiful.’ ” Those slings and arrows duly suffered, Hammond can concentrate on what is “a challenge for me”, she says, “to play the heroic lead. I usually play comic roles.” Those who saw Improbable Theatre’s The Hanging Man (2003), in which Hammond’s flirting with the audience stole the show, will know what she means.But here, it’s about getting the story right. The problematic ending has been improved, she reports. “We weren’t happy that the Beast changes into this smarmy prince.” This is meant to be a story that proves beauty to be only skin-deep, so why retain an ending that conforms to what Hammond describes as one of fairytales’ most interesting features: that “they use physicality to signpost evil. If you’re bad you will become ugly, or withered. But why can’t you be withered and nice?”

Or be small and play Beauty? Nothing vexes Hammond more than thethought that her size should determine the roles available to her. Since Told by an Idiot first cast her in 2000, she has turned down more than a dozen jobs in film and TV (where she made her debut as a 13-year-old in Grange Hill) because the parts have been, she says, “a height and not a character. To some people, you’re not a human and you aren’t an actor. You’re just a height. I’m not prepared to be that.”

Fortunately, she’s met people who are ready to be persuaded. For Channel 4’s Max and Paddy’s Road to Nowhere (a spin-off from Phoenix Nights), Peter Kay was looking for a comedic casting for the role of Max’s girlfriend. That he cast Hammond hardly denotes a progressive attitude to people of small stature. But when Hammond insisted on playing more of a character, Kay was quick to agree.

“It’s about how the world sees you,” Hammond argues. “It’s not OK nowadays to laugh at people with disabilities. But it’s still all right to wheel the dwarfs on, and go ‘Ha-ha-ha – funny little people doing the wrestling on children’s TV!’ ” And as for the likes of S now White and the Seven Dwarfs, “I couldn’t do it,” she says. “Because the moment I’d be on set with those little people around me dressed in elf costumes, I would go, ‘What the f*** am I doing here?’ ”Not all small performers agree. Now playing two of the seven dwarfs at the Darlington Civic are the veterans Big Mick and Pete Bonner, whose talents are advertised on the Dwarfs4 Hire website. “Comedy-wise,” says Big Mick, “for certain things you will use your height. Why not? If someone’s tall or fat, they’ll use that.” And, as he points out: “For Snow White and the Seven Dwarfs, you want seven dwarfs, don’t you? Snow White and the Seven Tall Personswouldn’t get in the cottage. They’d bang their heads.”

Both believe that attitudes have progressed in the past few decades, with greater challenges available to small actors. Bonner and Big Mick are the unapologetic pragmatists to Hammond’s idealist. But it’s in their interests that she continues the fight because “disabled actors are still where black and Asian actors were ten years ago. And for smallness, we are 20 years behind.”

Hammond’s burgeoning career suggests that there are still big roles to be had by small actors. “You just have to ask for them,” she insists. “And when you are told to come onstage, do a backflip, then run off, ” she grimaces, “give the guy two fingers.”

Beauty and the Beast, Lyric Hammersmith, London W6 (www.lyric.co.uk 0870 0500511), until Jan 5

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