When Alan Rickman is joined on stage by Vic Reeves, Eddie Izzard and Harry Enfield, you know that - unless the National Theatre's fad for star casting has spiralled out of control - there's a good cause abroad. For Amnesty International's 40th birthday, the quartet recreate Monty Python's famous Four Yorkshiremen sketch, the one in which they boast about childhood hardship.
It's among the evening's highlights, partly because the performers make one another giggle, partly because the moment recalls the illustrious history of the John Cleese-devised Secret Policeman's Balls and resonates as Something Special. Suddenly, in what first-on-the-bill Phill Jupitus refers to as just another benefit gig, we're watching a routine that wouldn't have been created for any other event.
Elsewhere, the extent to which the performers should adapt to the context is unresolved. While no one present would wish to be harangued, the show's status as a fundraiser for human rights - candles burning onstage post a constant reminder - makes certain acts look unfortunately trivial or complacent. At one stage, Jonathan Ross jokes about Geri Halliwell and Victoria Beckham's non-appearance. But when you've got Denise van Outen purring a Monroe-esque "happy birthday", you're in no position to jib at celebrity's superficial excesses.
Van Outen appears in a sequence of recorded inserts, alongside a gaggle of film stars and footage of U2 performing in Toronto. Back on stage, Tom Jones makes a tenuous claim for the appropriateness to the occasion of The Green, Green Grass of Home - after which one of the surprise stars, Sean Lock, quips: "I should get him to open for me more often." The peerless Harry Hill cracks a gag with a frisson, in which he shares a plummeting hot-air balloon with Hitler and Churchill. Well, who would you throw overboard? His uniquely manic energy illuminates the show's first half.
Hill's set is so enjoyable, you momentarily forget the Amnesty issue. A few performers broach it. Jeremy Hardy offers an unfashionable reminder that engagement with the real, as opposed to the surreal, world can be funny too. His asylum seekers material corrects the myth that human rights abuses all take place overseas. Mercury prizewinner Badly Drawn Boy strikes a welcome note of humility with two fragile ballads, the second of which is tailored to the evening's agenda. "There is no way to change the world in a day," he sings, then starts a Mexican wave. There may not be - but by uniting entertainment and cause, Badly Drawn Boy comes as close as anyone on the evening's bill to kickstarting the process.
