"The Naked Gag was supposed to be a one-off," says Mark Brailsford, The Treason Show's founder, artistic director and unofficial stripper. "When we started out in 2000, Keith Chegwin was launching a new naturist game show so, for a laugh, I ran on stage stark naked.

"Before the next show, there was a streaker at the Anna Kournikova match at Wimbledon so we thought, 'ok, one more time'.

"But the following month I wasn't in the show and everyone in the audience said 'yeh, it was funny but where was the naked gag?' So now we have to keep concocting reasons for me to strip."

As to whether Brailsford will be bearing all tonight, he prefers to "leave the question dangling" but he'll have a better excuse than usual for appearing in his birthday suit - The Treason Show is five years old and there's much to celebrate.

Founded in 2000 according to Bernard Shaw's dictum that "the best way to get an idea into people's heads is to shove it down their throats while their mouths are open laughing", The Treason Show is a monthly political sketch show which, probably uniquely, uses sketches, songs and one-liners to comment on local as well as international and national news.

It's the only sketch night where you can see a suicide bomber smoking a Hamlet cigar to the tune of Air On A G String, followed by a skit on the Falmer stadium; the only satirical team whose regular characters range from Ariel Sharon to Simon Fanshawe; and the only comedy show to imagine Saddam Hussein invading the Sussex coastline.

Joined in the past by the likes of Monty Python's Carol Cleveland, regulars Carol Kentish, Graham Lipscombe, Kate Van Dike, Mark Katz and Alistair Kerr combine comic, musical and improvisational talents with endearingly in-house impressions.

A team of 20 writers, made up of Brightonians and "strange little mole-like people who live in garrets", all contribute to the script, which is updated right up to the performance.

"Sketch comedy - and especially satire - had a bit of a tired reputation when we started," says Brailsford, "and I think we took it back into the 21st Century. Once you topicalise your material everyone connects to it.

With 24-hour news channels, people know what's going on so they identify more with this than with a circuit stand-up who has done the same act for two years."

The birthday shows will be reuniting the Treason Show team with some old characters, such as Hove grannies Winnie and Doris, who are getting very excited about the arrival of Brad Pitt. They'll be going to town on the Frank Gehry building and Falmer stadium and introducing us to La Maison de Treason, with their franglais reportage on the French vote for the European constitution. And you'll be seeing Saddam Hussein in his underpants as he tries to pip Abi Titmuss to a deal with Heat magazine.

Overall, says Brailsford, "we like to have a stab at everything". But there is, he says, one idea which, over the course of five years, they still haven't been able to shoehorn into a show.

"There's this guy who keeps sending us scripts for sketches involving a swarm of flies being released on to the stage," he laughs. "I can't really see that it has anything to do with satire and there's the whole issue of whether our budget stretches to training insects. Then again, it could become a cult favourite. Five years from now our audience could be saying, 'yeh, it was funny, but where was the swarm of flies joke?'"

Starts 8.45pm, tickets cost £7.50-£12.50. Call 01273 647100.