These are London's Cavalcaders, as the amateur extras are called. Cavalcade, Noel Coward's musical tapestry of 30 years, with its upstairs-downstairs tensions and tendernesses, has been on the road, gathering locals for its crowd scenes at each stop. A week's rehearsal, then on they go; two stage management companies overlap, one rehearsing up in Edinburgh, say, while the show is actually running down south. Volunteers are recruited via the local press, and responses vary. Manchester, City of Drama, fielded 180, for example, compared with Edinburgh's purse-lipped 70.
Coward's family saga manages to work in the relief of Mafeking, the sinking of the Titanic, World War One and the General Strike. The 1931 premiere had a real double-decker crossing the stage in the Trafalgar Square scene: among its volunteer passengers, the future Edward VIII could occasionally be seen. "It became the society thing to do," says director Dan Crawford.
Belted earls and princes of the blood are not noticeable in the John Cranko Studio at Sadler's Wells. I do meet Christopher, a musician with aspirations to acting, and Jade, immersed in theatre studies. She intends to apply for drama school after A-levels; he was a schoolboy in a "dire liberal" 1970s television film, Headmaster, which paid pounds 3.50 and "kept me in Marvel comics". "I'm only 17, so I haven't had time to do much," says Jade complacently.
Both were surprised to find so many familiar songs in Cavalcade: "Dolly Gray", "Soldiers of the Queen", "Tipperary". "I showed them the songsheet in a pub the other day," says Jade. "They were still singing after hours."
The old songs have struck a chord, evoked race memories, as Coward intended. (He naturally squeezed in one or two of his own, including the fiendishly tricky "20th-century Blues".) Christopher thinks longingly of "Don't Put Your Daughter on the Stage, Mrs Worthington" and "Mad About the Boy", but this is Coward in This Happy Breed mode: patriotic, nostalgic, even sentimental.
Dan Crawford detects a serious intent to the moist-eyed heart-tugging. "It's kind of patriotic but it's anti-war. It comes from the same school as Journey's End and The Silver Tassie." Coward acted in Journey's End, RC Sherriff's slice of demythologised trench warfare, and was inspired to Post Mortem, which "had rage".
Crawford is amazed that Coward figures nowhere in Jade's syllabus. "You may not like him, but his contribution to the theatre is as great as any this century. The Vortex shows a very 20th-century appreciation of the fragility of relationships. Private Lives, like every marriage in this country, is about people who can't live without one another and can't live with one another. He doesn't slide over pain. No one gets off easily in this play either. Maybe it's not patriotism he's talking about, maybe it's just non-cynicism."
Crawford is, of course, best known as the genial paterfamilias of the King's Head, the pocket-sized dinner-theatre behind an Islington pub. A resoundingly successful miniaturist, he has a good record of transferring productions to larger, more salubrious venues. But what on earth attracted him to the Cinemascope virtues of the epic Cavalcade? "I enormously like the idea of getting the community involved in the theatre - we all pay lip-service to it. I thought the best way of involving the community would be to put it on the stage." The idea of touring Britain with locals providing the crowds was there from the beginning.
And how have the locals responded? Wonderfully in Manchester, where volunteers included Mark (26), an amateur actor "with quite a bit of singing on the side" who wants to turn professional, and Sharon (29), a secretary who coyly replies "she has and she hasn't" when asked whether she has considered going pro. Her first work with professionals, she admits, makes for an exhilarating pace. "The whole place is different. There's a buzz."
In York, Katherine (33), who with Bootham no-nonsense calls herself a housewife, was brought along by friends. "I've had a brilliant time. I've done things I didn't think I could. I've learnt to waltz." At 58, Godfrey has more experience. His proudest claim is to have directed a show David Whitfield did in York six months before he died. The president of a local dramatic society, he thought the Cavalcade experience might give him insight into performing. "I would have been fully professional," he says wistfully, "if my parents hadn't thought it wasn't the done thing. I don't hold it against them... I've had various jobs. On the last occasion I was a hospital porter. A different sort of theatre."
According to Penelope Woodman, one of the professional principals, the character of the crowd scenes subtly varies from place to place. "In Edinburgh, with only 70 or 80, they really filled the stage with their presence. In a lovely old theatre in York, the smaller number of Cavalcaders made the play get bigger. In Manchester, it was more of a spectacle, so swept the audience along with it. When the Cavalcaders marched through the theatre in the war scene, the audience clapped along."
"Hello everybody! Costume fittings Sunday and Monday. It's a hell of a job for the wardrobe maker. Please, please, be as flexible as you can." In the Cranko Studio, the first lot of London Cavalcaders (there's a different lot each week of the three-week run) are licked into shape. "First let me introduce you to Alison, our pianist, who's absolutely lovely." The applause is slightly confused since nobody can find absolutely lovely Alison. We quickly cover for her by singing "Happy Birthday" to Alexander, nine today.
"Dockside people in here, seaside people wait in the opera studio." Jade plays a tart, apparently appearing all over the place. "There's one who thinks he's Pavarotti, that little guy hanging on to all his words," she says gingerly. "Everyone's really nice, but then I've only spoken to one person."
Dan Crawford resumes the task of "creating patterns by shifting numbers of people" and incidentally re-creating history. Outside London, the Cavalcaders were drawn mostly from am-dram societies, but the capital tends to offer more individuals. Over the three-week run, 900 are needed to flesh out the section of our island story between the end of the Victorians and the jazz age. "We're still recruiting. Say that when you print." Dan Crawford as Kitchener sends you over the top in Rosebery Avenue.
n Sadler's Wells, to 2 Sept (0171-713 6000)