What exactly does a costume designer do? With fashion designers like Jasper Conran turning their hands to theatre, the issue has become very confused. Deirdre Clancy is very clear that it's not just a question of running up glamorous frocks. 'A fashion designer comes up with a series of garments for a person to choose. A costume designer has to create and express characters through clothes. You're working on a text. It's an intellectual and interpretive process as well as a purely technical and artistic one.'

At one point she was designing three different shows in two countries with directors who weren't speaking to one another. Having survived the crisis, she decided to specialise. 'Costume design came easier. Perhaps it was a bit of a mistake. As a woman, it's rather expected. It can be difficult to persuade people that you can do the whole thing. But I'll do the whole shebang if asked.'

Her extensive CV boasts long working relationships with Christopher Morahan and Ian Judge. Her costumes were the high point of the recent RSC Love's Labour's Lost where her set designer was John Gunter. Together with Judge they are now ushering in the ENO Don Quixote, the latest production in the current Massenet revival.

Cervantes' novel was written the year after Twelfth Night but Judge didn't want a period production. 'It has become a 'trousers show', rather than a britches one. Given that John was working with very powerful colours, I've had the option of going for black and grey in order to be stronger than the set, or using even bolder colours. I've chosen the latter but it's risky. If you're not careful, it can look like a very bad production of The Student Prince.'

With 50 in the chorus - each with two or three changes - the chorus costumes are mass-produced on a semi-commercial basis. The costumes for the six dancers and eight principals are on a different scale and can cost up to pounds 500 to make, plus the material. 'They're show-off and fun but not at the expense of the piece. I've used neo-flamenco underskirts. It's a cross between Martha Graham and flamenco. I hope it doesn't come out looking like Ginger Rogers. I made a great slip while talking about it the other day. 'Of course,' I said to Ian, 'I'm frilled'.'

'Don Quixote' opens at English National Opera, St Martin's Lane, WC2, Sat 8 Oct (071-632 8300)

(Photograph omitted)