My name is Abdul ? but call me Trevor

In search of the Great British Joke The art of laughing at ourselves lives.

Heard the one about the comic who had to give an after-dinner speech to a room full of drunken welders? He almost got burnt as badly as a Tory MP.

The meal started with a moment's silence for those who had died in the rail crash a few hours earlier. Any remaining high spirits were crushed by the president of the London branch of the Welding and Joining Society with alleged jokes as heavy as lead piping. It was enough to make you feel sorry for a comedian, but Bob Curtiss is a pro.

He has been making people laugh in clubs, cruise ships, and dining rooms like this one at a hotel in Beaconsfield for more than 30 years. His judgement is not always perfect: the first joke is about a car crash and might have been funny on another day. The bad start gets worse when his microphone packs up – but this apparent disaster is the making of him. Suddenly the audience of more than 100 have to listen carefully, and even the hecklers on the Thames Welding Supplies table start laughing. Gags about sex, or otherwise, with the missus, and what it's like to be getting on a bit draw smiles of recognition. Bob is 63, and some of his jokes are at least twice as old, but the audience warms to his geniality. "My father was Yiddish and my mother was Irish," he says. "Half of me wants to get pissed and the other half doesn't want to pay for it."

Some people might be offended if they heard that joke outside this room, and his cheesy attitude to "the ladies" might not play so well if we were not all boozed-up blokes, but as far as Bob is concerned it's what works on the night that counts. He does not usually have to worry about how his material will look in the press, unlike the Conservative MP Ann Winterton who gave a speech to a rugby club last week and lost her job.

Bob Curtiss made his name in the 1970s, when people still called each other darkies and honkies on prime time television, so he knows how much British audiences have changed. Mrs Winterton found out to her cost that most of us do not consider the thought of throwing a Pakistani from a train funny at all.

"There are still people who think like that," says Bob, in the bar afterwards. "I don't think they've gone away. Most of them have just worked out that it's better to keep their mouth shut. She should have known that. The joke wasn't funny anyway. It was just nasty."

The Comedy Store in London is a completely different stage. Here the audience is young and multicultural. Yet Omid Djalili's comic tactics are similar to Bob's in one way: by making fun of his own ethnicity he seems to earn the right to do the same to others. The prize-winning comic who has a lucrative sideline acting as what he calls "an Arab scumbag" in the movies starts his routine with a heavy accent and a series of gags like this: "Most people associated the Middle East with oil, halitosis, and phlegm. Actually, we're running out of oil."

It works because he's Iranian – although when he slips back into his own British accent many people in the audience have a guilty look as if they've just been had.

"Ethnicity is a great source of humour," says Omid the next morning on the telephone. "There are things about different cultures that make us laugh. The best of modern British humour recognises truths about living in a multicultural society, and it should be inclusive and affectionate."

It's about us in the widest sense, laughing at ourselves. These days people from Pakistan and Iran are part of us (although Americans are not, judging by the huge number of anti-US punchlines heard at the Comedy Store).

After a joke that sums up the way we live now, Omid goes back to the first thing he ever said on a British stage, in 1994. "My name is Omid Abu Abdul Ghassem Ettehad Ibrahim Mambouhh – but just call me Trevor."