Until this week, the last political film to have moved me was Evita, starring Madonna, based on the musical by Andrew Lloyd Webber and Tim Rice. I know that sounds bad; there's no need to rub it in. Humming lightweight tunes about the exploits of a despot is about as endearing as supporting George Bush's energy plans. But happily - finally - a short film combining an irresistible mix of nostalgia, bravery and bloody-mindedness has wrestled my heart from the cynical clutches of Lloyd Webber.
The story of the Unity Theatre was screened in Soho to an array of elderly socialists, Trots and former music-hall stars. Harry Landis, for many decades an actor and director, began his career at the Unity. He introduced the tribute film by describing his own introduction to the theatre. As a factory worker, he had been told that plays were about "the terrible problems of the upper classes. Theatre wasn't a place for issues . . . or the working class."
The white heads around me shook and old mouths tutted in recognition. There were only four of us in the cinema who were under the age of 70. We stayed silent as the one-time communists hissed at the new world order and cheered the voices of dead colleagues, singing revolutionary songs from beyond the grave. "Sing me a song of social significance . . . let meaning shine from every line or I won't love you."
Unity Theatre came like a bolt from the blue in the early 1930s to shatter the popular view that the stage was a place of light and fluffy entertainment. Taking its lead from the work of "agitprop" groups in the Soviet Union and the plays of Bertolt Brecht, a group of amateur actors in King's Cross, London, created a company that bravely tackled social and political issues, using a mix of musical revue and hard-hitting satire. During the Second World War, the company's parody of Chamberlain reportedly made the PM "furious", and unsuccessful moves were made to close it down. One young actress was suspended from her job as a civil servant. She was followed by MI5 throughout the time she was appearing in the sell-out shows.
When firebombs smashed the theatre's roof during the war, the actors fought the blaze - and performed as usual the next day. Smaller shows were taken into factories and barracks, to remind workers of their rights and boost wartime morale.
The actors Bill Owen, Michael Gambon and Warren Mitchell recalled their days at the Unity with fondness. Michael Redgrave and Herbert Lom had also spent time in the icy little hall.
Throughout, the cinema audience was reminded of a misty era when the labour movement represented the interests of the working man. They recalled bygone days before left-wingers became "wreckers", when helping the poor and supporting unilateral disarmament were the Labour Party's raison d'etre. I had a lump in my throat by the time the credits rolled.
Parts of the short film had us laughing with recognition. One show at the Unity parodied the Attlee government. Why? For sucking up to City bankers and traders at the expense of the working class. Worse still, who would have believed that a British prime minister would become such a willing slave to US foreign policy?
Mutters of "Shame, shame" echoed around the auditorium.
History is being rewritten, and groups such as Unity are in danger of being edited out altogether - or perhaps, more insidiously, of being sanitised out of existence. They deserve recognition, and someone should chronicle their incredible story.
If only Ben Elton had not been seduced by the evil Lloyd Webber and George Bush! Instead of crying through the opening bars of "Don't cry for me, Argentina", I might be thrilled by a musical with a bit more historical accuracy . . . a musical about Unity Theatre, perhaps?