Joan Littlewood's classic satire of the First World War, Oh What a Lovely War, is back in action, touring Britain in a circus big top. David Benedict watches the drama unfold in a field in Swanley. Photographs by David Modell
S Eliot got it wrong. March, not April, is the cruellest month. Cold, windy and wet is not the ideal weather forecast when you're trying to open a national tour of a giant show. In a tent. Or rather three of them: a foyer tent, a bar and a big top seating 750 people.

The show in question is Oh What A Lovely War, the cross between a musical and a docu-drama about the First World War that began life in the mind of Joan Littlewood, born in Stockwell in the year that the war broke out. Littlewood's massively influential Theatre Workshop, which she founded after the Second World War and which eventually made a permanent home at the Theatre Royal Stratford East in London, created the fiercely satirical Oh What A Lovely War in 1963. It proved so successful that it transferred to the West End for a long run; Richard Attenborough made his directorial debut with the film version. The vigour, clarity and dramatic immediacy of the play have made it a staple of school productions and the more ambitious amateur companies, but London has not seen a professional production since the premiere.

When director Fiona Laird wrote to Littlewood enquiring about the rights to Oh What A Lovely War, she had no intention of embarking on a vast and complicated tour of England. Richard Eyre, then still the artistic director of the National Theatre, wanted Laird to mount the show on the South Bank, but Littlewood's antipathy to that cultural empire was well known. Laird says Littlewood's opposition to the National can be summarised as "it's a middle- class, elitist institution which takes something away from the regions"; so Laird tried to mount the show at Greenwich, but the scale of the piece proved prohibitive. By this time, Littlewood was so enamoured of Laird's approach that she allowed her to hold on to the rights.

Trevor Nunn, Richard Eyre's successor at the National, told literary manager Jack Bradley that he wanted to do the show - so Laird came back into the frame with her dream project, and Nunn came up with the idea of doing it with National money but outside the building. Littlewood's response was forthright but positive: "You can take money from the devil, just so long as you get it on." The result is a three-way production between the National's touring education department, local councils across the country and tent show specialists Mamaloucos Circus. Which, one year later, brings us to the first venue of the tour: a dank, muddy field behind the community association building in Swanley in Kent, a world away from Sir Denys Lasdun's cool grey, modernist South Bank landmark.

You can see the tent from the train station, an eerie, timeless construction of white Italian canvas marooned amid the local shops and housing estate. With six days to go before the opening, two circles of white pegs mark out where the second and third tents will be. A driver is in the middle of an eight-hour round-trip to Shropshire to pick up the poles. It's a problem. You wouldn't normally expect to be building the theatre at the same time as trying to run technical rehearsals on stage. And that will happen every time they up sticks and relocate to another part of the country.

In a thick black coat and scarf, Jenny Harris, the National's head of education, is putting a brave face on it. You can see the tension on her forehead but she exudes warmth and confidence. She's excited by the collision of all these different worlds. "There's the theatre side of things meeting the world of new circus; union and non-union labour, the work of the local authority." All rife for demarcation disputes, I suggest. She points to the stagger-through the company gave last night in the shell of the tent. "In the face of all this chaos, it suddenly all made sense. You could see everyone's respect for each other growing."

Inside the tent, it's clear what she means by chaos. Above the steeply raked stage, the lighting rig is up and a couple of giant working lights illuminate the cavernous, swagged, dark red canvas that engulfs us. It's the lunch break and the pianist is noodling some Steely Dan behind the set and actors are wandering around nursing shopping bags from the nearby supermarket, where they appear to have taken up second home.

At this point in a production, it's fine if the auditorium is strewn with coloured lighting gels, sound equipment, props and pieces of costume, but you would expect most of that to be lying on the seating. Alas, they're still waiting for the seating. Fiona Laird sends out for fruit juice and 60 cigarettes but seems remarkably perky given that they're three days behind schedule. She kicks away some matted, muddy straw soaking up the mud and smiles surreptitiously. "If we'd stuck to the schedule, I'd be worried, but I cunningly brought the technicals forward by three days because I never believed it would happen. That's because I lived through the nightmare of the National's Peter Pan technical."

As the company manager rings a handbell - shades of school - to summon the cast back for the afternoon's rehearsal, an actor returns from a food run in full make-up. "Yes, I went to Asda like this. Yes, I got comments. No, I don't care," he beams before disappearing to prepare. Even though they're all less than warm, spirits are high and you feel that as long as the sound problems can be overcome, they'll be happy. After the intimacy of the National's rehearsal rooms, the tent's acoustic has come as a shock and radio-mikes have had to be ordered. The float- mikes at the edge of the set in last night's run picked up nothing except the sound of the company's feet. Peter Darling, the choreographer, is reported to have spent the entire evening with his head in his hands.

Laird, however, is raring to go. She's a powerful advocate for the play. She believes it to be unique. "There are other pieces about the First World War, but nothing else covers it in its entirety. It's immediately engaging, very powerfully moving, but it doesn't spoonfeed audiences by telling them what to think. It leaves a lot to their imagination. It's set in a theatre with Pierrots putting on a show and it only works in a theatre. Look at the film."

She's right. Like Attenborough's later failed attempt to relocate a supremely theatrical musical to film with A Chorus Line, his movie is galumphing and entirely misconceived. Film is too literal a medium for the piece. It shows you everything. Your imagination is left dormant except in the tremendous final crane shot, which pulls back to reveal a sea of white crosses on the French battlefield. By contrast, theatre demands that an audience does some work. It plays with your imagination by having the cast play actors who, in turn, play everything from nurses to mothers, foot-soldiers to generals. The unifying factor is the use of documentary material, which is projected against the action: statistics, images and information about the war, plus the ironic use of songs from the period. It's a British musical steeped in the British theatrical tradition set precisely at the point before the Americans arrived and made their mark on popular culture.

The end result should be startling, and profoundly moving in its complete avoidance of sentiment. If Laird and her company - and the 45-strong circus crew - get it right, Littlewood's vision will have been reborn in different but peculiarly apt circumstances

"Oh What a Lovely War" is at Thurrock tonight (box office: 01375 383961); Milton Keynes, 31 March- 4 April (01908 583928); London, Oxo Tower Wharf, 8-25 April (0171-928 2252); Brecon, 6-9 May (01874 611622); Telford, 12-16 May (01952 619020); Dewsbury, 19-23 May (01484 221913); Chester, 26-30 May (01244 340392); Richmond, 2-6 June (0181-940 0088); Tedworth House, Tidworth, 10-13 June (part of Salisbury Festival: 01722 320333); Nottingham, 16-20 June (0115 941 9419)