Comedian Benny Hill pushed the boundaries of political correctness

Professor Christie Davies of the Social Affairs Unit think-tank has published a pamphlet, The Right to Joke.

He told BBC Radio 4's Today programme jokes were necessary to relieve tension and subvert established orders.

But he warned political correctness was making many joke-tellers hesitant about sharing their humour, as he once observed in communist eastern Europe.

Having seen one half of the world going crazy, I don't want our half going crazy Professor Christie Davies

He said on a recent trip to north America he had discovered an unwillingness to share jokes, reminiscent of those who used to live behind the iron curtain.

"What shocked me there was the extent to which employers will monitor automatically and scan people's emails to make sure they're not exchanging jokes.

"I also found that when I was collecting jokes from people, they were as nervous about telling me jokes as the people had been when I collected political jokes in Bulgaria in the communist period."

Joke 'snooper'

Professor Davies told the programme that joke books in Canada started with an apology stating their content was not intended to offend anybody.

HAVE YOUR SAY Telling jokes is part of the coping mechanism, it's how we know we can relax and trust each other. Jack Howard, Leeds, UK Send us your comments

He said he was concerned the problem might cross the Atlantic to Britain.

"Having seen one half of the world going crazy, I don't want our half going crazy."

"What I'm worried about is finding the same phenomena of people being nervous to talk to me about jokes, looking over their shoulder."

He put their reticence down to the fact that he spoke "educated" rather than "vulgar" American.

"As soon as I turned up and spoke 'educated American', people assumed I was some kind of snooper".

Disaster humour

In eastern Europe... even the powerful people told jokes about themselves because they wanted time off Professor Christie Davies

Asked if he would advocate jokes on topics such as the Morecambe Bay tragedy being aired, Professor Davies said he saw no problem with such jokes going to air.

"If you had a comedian and you gave a warning in advance, why is that any different from all the television [broadcasts] you put out that are full of obscenity?"

Being able to speak in only one acceptable way about a subject made people so tense they wanted to tell jokes, he said.

Explaining the black humour that arose after disasters such as the Challenger shuttle exploding, he said: "You have a dominant, hegemonic mode of speech about something.

"As soon as you establish that, people try and sneak round it.

"What was striking in eastern Europe was that even the powerful people told jokes about themselves because they wanted time off."