Dear Tilda Swinton

To the actress - sorry, performance artist - contemplating lying in a glass coffin all day: don't, it'll be deadly dull for you and plain deadly for the rest of us

I know you're terribly busy preparing for your new show (oops, sorry, installation) at London's Serpentine Gallery, but there are still a couple of weeks to go and I have a suggestion. Get the hell out.

Acting is a dreadfully undignified profession at the best of times without you making difficulties for yourself by lying in state in a glass coffin eight hours a day. The Maybe, you call it. Maybe not. Equity members fought for years for statutory working practices without you lying about doing still-life performance art while demonstrating a lofty indifference to the odd cheese sandwich or loo break.

Unless you are one of the handful who idle away their days turning down choice leading roles, actors spend their time waiting for the phone to ring. In terms of the number of roles available, it's far worse for women and, all in all, it's no life for a grown-up. Small wonder that actors turn to creating their own work, but tell me, Tilda, is this the answer?

Many of us have sat through dire solo shows devoted to the minor scribblings of Bloomsbury blue-stockings and if I ever have to sit through another piece based on the life and death of Sylvia Plath, I shall scream, but both these alternatives seem like dramatic manna from heaven in comparison. It may stretch your bladder, but I fail to see how it will stretch you as an actor.

Oh, I forgot. Despite winning a Best Actress award for your terrifyingly beautiful Queen Isabella in Derek Jarman's Edward II or stretching everyone's ideas of gender in Orlando or Manfred Karge's powerful Man to Man, you're not an actress. Silly me, you're "a performer" and most of what you do is "deeply autobiographical", which sheds an interesting light on your magnificently flouncing Lady Ottoline Morrel in Jarman's Wittgenstein.

I saw one of your "performances". It was a special preview of Derek Jarman's The Garden, horribly early one morning. Prior to the screening, you and Derek sat at the side of the stage intoning the odd word to accompany what could loosely be described as "some dance" accompanied by a suitably impenetrable score. The cinema did a spectacular trade in snacks as the entire audience rediscovered the meaning of the word boredom. The net effect was to deal a death blow to the interestingly fragmented film. We'd already had our fill of fragmentary.

I can play post-modernism with the best of them and Snow White - the life and times of a woman who winds up in a glass casket - is a smart place to start. But don't you think you're going a bit too far? People will witter on about whether this is art but I, for one, do not care. Your press release tells us that it will be "a performance of epic proportions and contemplative beauty". It sounds to me like a waste of our time and your talent.

Yours regretfully,

David Benedict