Joining the King's Head touring production of Noel Coward's Cavalcade, the first thing to remember is not to get on the wrong side of its hundreds of unpaid stars. You can upset them quite easily by bracketing them with the sort of people who make a quick fiver by walking up and down high streets, clutching shopping in police TV series.
The process which distills crude recruits into refined Cavalcaders may only take a week of evening rehearsals, but it is a hard one. Hard by the standards of the am-dram societies where anything less than six months' preparation is considered positively breakneck. Hard because Coward intended the piece to be an epic chronicle for the nation. There are 22 scenes running from the turn of the century to 1930, most requiring large crowds, ensemble singing and costume changes with attitude.
After being split into groups and pummelled into shape by two assistant directors, we are now at dress rehearsal stage. Time for a soothing chat from the director, Dan Crawford: "You are all essential," he says. "Without your being absolutely on the mark, this whole event will be off the mark." Naturally, a few nerves are set jangling. "We're standing here like this," an elderly man whispers, "but how do we know that this is how they would have stood in those days?".
As a rule, it is best to avoid the detail-mongers and find those with a broad grasp. "You go on. There's a song. You go off," a Mancunian lad called Dave informs me. For reasons of morale, it is wise not to participate in the camp badinage that burbles, fountain-like, in the background: "Could you sit down properly in the front, or I'm afraid we'll have to cut your head off," for example, or "hang about, Queenie's going to make a speech...".
For the same reason, block your ears to backstage moaning. Three women in Victorian, ankle-length skirts mutter darkly among themselves. "We've bought two tickets for tomorrow," one says. "And now my friend can't come, so that's pounds 7 down the drain." "There should be four prompt-letters," chimes in another, "but there are only two. You have to make them yourself - it's pathetic." "Anyone can go on that stage - anyone," despairs a third.
Ignore them. Calm absorption is all, and calm absorption is what we get on the first night. Men and women, young and old, quietly slide in and out of period costumes in the changing area behind the stage and, un- cued, troop on and off: a dockside fight, the Boer War, the death of Queen Victoria, it all goes tickety-boo.
Before I know it, I'm on "the beach of a popular seaside resort", in 1910, in summer blazer and boater singing "Oh I do Like to be Beside the Seaside". I have to wave at fellow holidaymakers, mime small talk and look astonished at a plane flying overhead. React, react, then off. Simple. Hardly feels like acting. Scarcely time to register the historical tapestry woven by "It's a Long Way to Tipperary" and "Roses of Picardy" before I find myself in Lithuanian Army uniform celebrating the end of the First World War in Trafalgar Square, opposite Worsley Opera Society's Lil Eckersley and her daughter, Louise.
The feeling at the end is euphoric, the sense of community prompted by the programme credits, palpable. For Bill Owen, Granada Studio Tour's funny man, it's a 40-year-old dream come true. Sharon Brody, a sales rep, has just one quibble: that the leads are a bit "stuck-up". "I worked with Julie Walters as an extra and she was ever so sweet, came over and talked and everything. This lot... I mean, I know we wouldn't be there without them, but at the same time, they wouldn't be there without us, would they?" She says this firmly, as though to add anything else would be simply extraneous.
'Cavalcade' to 2 Sep, Sadler's Wells, Rosebery Avenue, London, EC1 (0171-278 8916). Details on being an extra: 0171-226 8561