Wax's witching hour

For a famously loud-mouthed lady, Ruby Wax has been unusually quiet of late. That's partly because the US comedian has been shut in a cupboard in Nottingham for the last three weeks, rehearsing her role as Grand High Witch in the new stage adaptation of Roald Dahl's The Witches.

'It's been real bizarre,' she confesses with trademark brash candour. 'Because it's a touring production, the rest of the cast are off doing the show. I'm only in the London weeks, so I'm alone in this little room with the stage manager playing all the other parts.'

Based on Dahl's classic about a seven-year-old boy and his magical grandmother, who battle a worldwide witch conspiracy to poison children's chocolate, The Witches is the first time Wax has trodden the boards for 20 years, after an early stint at the Royal Shakespeare Company failed to propel her to stardom. 'I never carried a spear but I was a nun and a whore for a long time.' So, is she nervous about now being what she calls 'the main gig'?

Hard to tell. Partly because, although she is an outspoken and provocative interviewer, Wax is a rather cagey interviewee, and partly because she is yakking to me on the phone through regular forkfulls of salad. 'I'm trying to no-carb,' she groans, crunching into something that sounds suspiciously like a crouton. 'See, I've gotta fit into this cauldron...'

Cauldrons are just a drop in the ocean in this fantastical production, crammed with illusions by Paul Kieve, the effects wizard who worked on Harry Potter And The Prisoner Of Azkhaban.

Wax's costume ('I commissioned it specially from Maria Grachvogel. She's my guru. Now I've got to fit into that too...') is topped off by Childcatcher-style make-up. 'It's still being worked on but I know it's great - really camp and nauseating. My head is bald with scabs all over it - and I've demanded that I can spit blue spit, too - like in the book.'

It sounds like the perfect panto role for larger-than-life Wax, still best known in Britain for her outrageous Ruby Wax Meets..., where she would get the inside grubbies on such A-list divas as Imelda Marcos, Liza Minelli and Fergie.

Great material to draw on - so spill: who is she basing her Grand High Witch's witchiness on? 'Me![spoilsport]

I remember Angelica Houston in the film version not being scary enough. We all have our own inner witch; mine's much more Witch of the West. I was born to play this role.' So, does this mean more theatre?

'Man, I would hope so but I don't think so,' Wax says, mood-swinging from her usual look-at-me persona to an engagingly wobbly actress.