Mark Thomas says he used to be a stand-up comedian. Now he doesn't know what he is. Satirist? Campaigner? Probably both, and from three rows back at the Soho Theatre he is also a convincing Ken "Rebus" Stott lookalike, all bulbous eyes and attitude. And, in Thomas's case, lashings of lacerating wit.

His enlightening show is essentially a live edit of his recent book, As Used On The Famous Nelson Mandela (Ebury), in which he exposes the chillingly mundane business of arms dealing. This is a bizarre world where, we are told at breakneck speed, anyone can buy electroshock batons on the web, holster optional.

Thomas divides his set into five frenetic acts. The warm-up is less guns, more mutter, as he reveals his fiendish plan to irritate the police by staging lone demos in Parliament Square. He has already had a dry run, waving his placard in defence of surrealism: "No slogans, just wallpaper".

There is plenty of surrealism when he addresses his main agenda too. For Thomas the munitions industry has all the dream logic of a Dali landscape. A trade fair is vividly portrayed as a moral vacuum where buyers of weapons are offered muffins by pouting models.

The show's highlight is the tale of meeting Mick Ranger, who supplied the umpteen Kalashnikov used in the Hungerford massacre. Ranger is a true black belt in ethical doublethink, marketing murderous tools but unwilling to shoot animals. Thomas's powerful finale - politically stronger, though comedically weaker - exposes further Kafkaesque absurdity in surprisingly high places.

This might sound dry but it never is. A sweaty impression of an indignant cluster bomb salesman is particularly priceless. The fact-packed 90 minutes could be trimmed, but Thomas has lots to say. Perhaps for his autumn Tricycle run an interval would be as welcome as the free reading matter distributed at the end.