An out-of-control rock singer stomps up and down, pouring water over her head. Two clowns consider the universe. A girl in a gorilla suit hopes we are thinking of making love to her. Two naked men holding silver cardboard stars compare the beautiful silences of a quietened baby and a switched-off life support machine. An actress in a red satin dress says: "When I lie down, you are going to cry for the rest of your lives."

It all makes a nice change from Chitty Chitty Bang Bang, and marks the 20th anniversary of the Sheffield-based performance group Forced Entertainment. I last saw the company in 1987, when it was striking out in a disturbing new direction of post-apocalyptic alienation. Today it is regarded abroad as, quite simply, the best of British.

Theatregoers of a certain disposition in Paris and Vienna, Beirut and Zagreb, could not give a hoot about Alan Ayckbourn or the Royal Shakespeare Company. "Bring us the latest of Forced Entertainment," they cry, and will not rest until the stage is littered with rubbish and the actors are consumed with despair. I am in two minds about this. Catching Bloody Mess at the buzzing Warwick Arts Centre - the show plays in the Lift "Indoor Fireworks" season at the Riverside Studios in west London before resuming its triumphant national tour to Brighton, Glasgow, Aberystwyth and Manchester - I found myself swept up in the stage atmospheres while being simultaneously irritated by a steady stream of metaphysical banalities and a limited physical expression.

There is no doubt that the business of "making theatre" from scratch is where Forced Entertainment excels. The director, Tim Etchells, and his team - they have all been together since student days at Exeter University - lay down various narrative strands that derive from human predicaments. The actress is in the wrong place. The clown is not funny. The singer, who resembles Janis Joplin on a bender, cannot master the music. The gorilla girl is a bundle of sexual vanity and psychosis.

Where Ayckbourn would, or might, constrain these crises in a situation comedy, with conventional scenery and a recognisably English kind of acting, Forced Entertainment explodes outwards into the theatre. Narrative becomes a means of describing not just the spiritual condition, but also the circumstances of performance.

So the action is defined by the stock visible parameters of the costume rack, the table with the bottles of water, the on-stage lights, the sound equipment, the ever-present long-haired technicians, the audience. The actors address their remarks more to us than to each other. The gorilla moves through the auditorium handing out tissues.

Bloody Mess begins with a farcical and cumulatively hilarious battle of wills between the clowns, who play tug-of-war with a row of chairs. When the ten chairs are finally arranged in a line, the ten actors sit down and declare their identities. This is the most striking part of the performance. While absorbed by the rest, I was disappointed in the level of physical "finish" to the movement and "profile" of the characters.

For all its intelligence and cheek, this is not in the same class as the best of Pina Bausch, or even Wolf, that astonishing Belgian dance drama that came to Sadler's Wells a few weeks ago and combined modern anxieties and outrage with a most exquisite level of technical poise and execution. Apologists will say I am missing the point. What is refreshing about Forced Entertainment is that, even after all this time, it is playing with theatre, adding quirky footnotes to the helpless nihilism of Samuel Beckett, searching for new metaphors.

One way of looking at Bloody Mess is as the deconstruction of a rock concert. The most voluble clown is finally expelled from the band while the other is reduced to doing impressions of weapons and animals. One of the nude starmen plucks an acoustic guitar quietly in the corner while the actress repeats, mournfully, that she is the last thing we shall see.

Because the control of mood and dynamic is so strong, it is impossible to dislike or dismiss the show. Its ragbag randomness is transformed into a sort of aesthetic virtue, and you get to like the performers more than a little. The text, aside from the tedious existential bits, is ironic, philosophical and fairly funny. I just wish there was more to admire in the physical attributes of the performers, and I am not being smutty. In zoological terms, they are domestic animals, not jungle beasts. They are cats and canaries, not tigers or tyrannosaurs.

The Warwick Arts Centre has exactly the right ambience for such a show, with its relaxed and comfortable facilities, its mainly student audience, its cutting-edge feel. It was so long since I had been there that I had forgotten the sheer range and splendour of what is on offer. Two theatres, a cinema, a concert hall, a gal- lery, restaurants, bars and shops. And in one week you could have seen not only Forced Entertainment, but also Merce Cunningham, Bill Wyman, six kids' shows and the City of Birmingham Symphony Orchestra.

The Midlands are on the march, with new theatrical alliances being forged between Warwick, the Royal Shakespeare Company in Stratford-upon-Avon, the rejuvenated Birmingham Rep and the remodelled Belgrade at Coventry. Seeing Forced Entertainment in such a context seemed both emblematic and challenging. Is this acclaimed company still proclaiming the future, and if so, how can we improve it?

Bloody Mess is at the Riverside Studios, London W6 (020 8237 1111) until 5 November, then on a national tour (0114 279 8977 or www.forced.co.uk)