Declan Donnellan and Nick Ormerod are Cheek by Jowl - a company where collaboration is everything. Will their latest show be their last?
Even the most clued-up commentators have a hard time sorting out who exactly did what on a production. A great set is routinely attributed to the designer but maybe it was the director's idea. The effortless staging of a show may in fact be the result of the organisation of the space by a cunning designer. Look at the Royal Court's Cleansed, for example. Its bloodied but unbowed writer, Sarah Kane, has come in for all sorts of attacks but director James Macdonald and designer Jeremy Herbert have been feted. But are Macdonald or Herbert responsible for the hypnotic realisation of Kane's images? It's the same with the multi-award-winning An Inspector Calls. Who came up with the visually compelling metaphor of the house collapsing in front of our eyes - director Stephen Daldry or designer Ian MacNeil? Does it matter?

The deliberations of awards committees aside, such demarcation disputes are, for the most part, a trifle academic. These productions succeed because of their enviable seamlessness. But if the blurring of roles produces such strong theatre, where better to examine it than in the international success story which is Cheek by Jowl.

The company is the dreamchild (or rather, fully-fledged adult) of Declan Donnellan and Nick Ormerod, nominally its director and designer respectively. But the truth is nothing like as simple. Much Ado About Nothing, their latest - and maybe their last production - sweeps into London tonight at the end of a tour which has already taken them around the country and as far as New York, Barcelona, Rennes, Strasbourg, Recklinghausen and Stockholm. When they played Moscow, the curtain went up late because so many people were packing themselves into the Maly Theatre. When the applause had finally died away and everyone had gone home, they realised the weight of so many people had cracked the balcony. The boards outside the Playhouse Theatre are emblazoned with glowing reviews from the world's press, but, taking time out from getting the set in, Ormerod remarks upon a comment by New York's viperish John Simon. He bucked the trend and took against the production, which Ormerod has no problem with. What gets his goat is Simon's view that its supposed failings stemmed from the fact that the company is breaking up because Donnellan and Ormerod were, too. Neither is true.

They met as Cambridge law students acting in a production of Macbeth in 1972 and, according to Donnellan, since sharing a Chinese takeaway on the second night of rehearsals they have been inseparable. They moved in together after university and formed Cheek by Jowl in 1981. Kicking off with Wycherley's comedy The Country Wife, they moved sideways with a striking adaptation of Vanity Fair before settling down with a mix of Shakespeare comedies and tragedies interspersed with lesser-known European plays.

From the word go, they overlapped. As Ormerod explains: "We choose the plays together, produce and cast them together. I go to as many, if not all, the rehearsals. Not that I would dream of talking to an actor about his performance." That clearly is Donnellan's department. What they don't do is sit at home carving out the interpretation in advance. There are no pre-production meetings about "the concept". Everything happens in the rehearsal room. The flipside of this collaborative approach, which allows the actors, the movement director and so on to shape the production, is that, when push finally comes to shove, it has to be designed very quickly - "often over a weekend". They rehearse for six weeks, the first two being spent discovering the depths of a text or, as Ormerod deceptively describes it, "messing around". Then radical decisions are taken.

In the case of Much Ado, this amounted to deciding to set it in 1900, turning it into a specific and ambitious costume piece. It's a play about men returning from war. We're talking uniforms. The choice of period points to another key element in the work. Unlike many other companies, the decision for Cheek by Jowl is always why not do it in modern dress? Twentieth century war, however, is a completely different animal. They improvised and played around with ideas about the First World War but that set up inappropriate ideas of field hospitals and the like and didn't begin to answer the question of the women in the play, not to mention the comedy's dense language.

At which point, all sorts of other associations came to the fore. Linguistically and dramatically, the play is obsessed with overhearing, whether it's the famous hoodwinking of Beatrice and Benedick or Claudio believing Hero to be faithless. Both director and designer felt the set must articulate that, allowing people to be hidden or watching and listening off-stage. Picking up on the formality of the period, they've turned much of the action into an elaborate ball and staged the first four scenes as a kind of tea party which exploits the Oscar Wilde atmosphere of the time. "It's there in the Comrade and Borachio plot: the dirt beneath the glossy surface." They also believe the play's only really happy marriage is Beatrice and Benedick and that Don Pedro's love for Claudio is the key to the piece. "It's undeniably central," asserts Ormerod, "it's in the text." From the company that ignited the sexual politics of As You Like It in their outstanding all-male production, this looks like a fascinating proposition.

Beyond the interpretation, there is a scintilla of truth to John Simon's presumptuous comment. They're still a couple, but they're taking an open- ended sabbatical from Cheek by Jowl. Producing an annual world tour of a new piece with only enough Arts Council funding to run a three-person office and play five weeks in England is a killer. Ormerod and Donnellan are the company, which makes nonsense of handing over to another team, so they're putting it on the back burner to venture out into the big bad world of freelance life.

It's not a wholly new experience. They had a hard time on Martin Guerre but won awards for Angels in America and Sweeney Todd at the National. Intriguingly, it is there that they've had their biggest rows. A large- scale theatre like the Olivier requires designs to be submitted three months in advance of rehearsals. "If I give Declan an empty space, I know we'll be alright because he and the actors can sort everything out. When we did Peer Gynt there, I knew there were all sorts of problems that were only solvable by me. Declan is just terrible at sitting down with a set model. He says, 'yes, that's great' and walks out of the room. On that occasion I needed a bit more."

Ormerod has occasionally worked outside their relationship, most recently doing Strindberg at Leicester Haymarket, and, as we speak, Donnellan is in Paris working with a French company on Le Cid. It's the latter set- up which is more of a threat to their relationship. "I understand the difficulties of a total commitment to one designer. There's no skin off his nose if I work elsewhere," observes Ormerod, evenly. "But if he starts looking down the list of designers and starts working with someone else on a regular basis, I might have something to say about that."

Playhouse Theatre, London. Bookings: 0171-839 4401.