“Never respond to critics,” was the advice a playwright gave me many years ago. “It’s like feeding rats,” he said, and it’s advice I’ve always taken, until now.

The critical response to my adaptation of Midnight Cowboy has made me break my chaste vow of silence. It’s not that the reviews have been bad (far from it) but because some critics believe that adapting a movie for the stage is intrinsically wrong.

Benedict Nightingale writing in The Times, while comparing our two leading actors favourably to Jon Voight and Dustin Hoffman (who played the original Joe and Ratso in the movie) questioned the point of a stage adaptation at all while the DVD was still available. Quentin Letts in the Daily Mail, while also singing the praises of the actors, went even further and said the big audiences going to the show were “sheep”.

Throughout history playwrights have retold and repackaged the stories of previous generations. Take away the “borrowed” plots and characters from Shakespeare’s work and you’d be left with a much thinner first folio. Without the Pygmalion myth George Bernard Shaw’s 1916 play would never have existed and there’d have been no My Fair Lady. Without Shakespeare’s Romeo and Juliet, West Side Story would have been a set of songs in search of a plot. No theatre critic begins a review of Hamlet by saying “yet another production” (though perhaps they should) or bemoans the fact that everybody knows the ending.

So to attack us for re-telling, for the first time anywhere in the world, James Leo Herlihy’s truly great and bizarre love story strikes me as a bit rich.

A huge number of recent shows — think Billy Elliot and The Graduate, The Postman Always Rings Twice and The Lion King — were inspired by movies. The reason they are so popular is that the 20th century was the century of the cinema. The myths that appeal to us most profoundly are celluloid myths.

The cross-fertilisation between books, plays, classical myths, popular music, television, film and the internet will continue because it’s the way the current generation sees the world.

We live in a much more eclectic and less rigidly structured society than our parents and we are all the better for it. To refuse to acknowledge this is a bit like a restaurant critic rejecting fusion cooking — and we can all remember the joys of eating out in Britain before we started to use foreign ingredients.

So, dear critics, by all means attack me for my rubbish northern writing, have a go at me for my graphic sex scenes (apparently we didn’t get to see the boys’ genitals as much as the girls’), even criticise me for my performance between the sheets (you know who you are), but don’t tell me and more importantly don’t tell audiences who are queuing round the block for our show that they shouldn’t be there.

If you want to see what happens when a festival is programmed exclusively by the arbiters of high art you need only peek at the accounts of the Edinburgh International Festival. It ran up a deficit of more than £1m last year despite an extra £600,000 in cash from Edinburgh city council and EventScotland.

There are two types of theatre: good and bad, and all other distinctions are simply the product of narrow-mindedness and snobbery.

Midnight Cowboy is at the Assembly Rooms, Edinburgh, 1.15pm until August 28. Box office 0131 226 2428

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