Prepare to be amused

AJP Taylor famously said: "History gets thicker as you approach recent times." So does comedy. When, as part of the London Comedy Festival, London Underground, South West Trains, Connex, Thameslink, Thames Trains and Anglia Trains offered to donate £100,000 worth of advertising space in their carriages to a selection of modern jokes, they promptly received a deluge of witticisms from the festival organisers.

Commuters will note that the series - which goes under the banner Mind The Gag - contains no jokes about late-running trains. A busking joke has crept in, but it's clear that it's not one of those problematic Underground buskers. Policeman: "Excuse me, sir, but do you have permission to play the violin in the street?" Busker: "Well, actually no." Policeman: "In that case I must ask you to accompany me." The busker then delivers the punch line, which you may attempt the small - very small - challenge of guessing.

And there are no really mucky jokes. The list did include a gag by the lugubrious London comedian John Moloney about how he had an affair with a posh bird "and caught a dose of lobsters". That was rejected, but, by way of compensation, another gag on the seafood/sex interface has made it on to the carriage walls, courtesy of Billy Connolly: "Have you heard the one about the oyster who went to the disco and pulled a mussel?"

In the face of their public-spiritedness in allowing Mind The Gag to go ahead, it's impossible to begrudge the railway executives their small acts of censorship. Why should they lay themselves open to the possibility of letters of complaint? But then again, I Have A Gentil Cock - an incredibly disgusting 15th-century poem - appeared on Tube trains in 1990 as part of the Poems On The Underground series, and not a single eyebrow was raised.

Poems On The Underground has gone down well with the travelling public, and London Under-ground is sure that the Mind The Gag posters will do likewise. But can they pass the severest possible test: raising a smile from rush-hour commuters?

We all know that delicious feeling when you can't stop a smile in a crowded railway carriage. The last time it happened to me, I was returning from interviewing the brilliant American comedian, Steven Wright, and thinking about one of his lines: "I bought a decaffeinated coffee table." That's not on the approved list, but another of his bon mots has made it: "I was hitchhiking the other day and a hearse stopped. I said, 'No thanks, I'm not going that far.'" The London Comedy Festival runs 18-26 May. For more information call 08700 119611 or visit londoncomedyfestival.com