Image caption I say, I say, I say... would you buy a used joke from this man?

Keith Chegwin has come under fire for allegedly plagiarising other comedians' routines. But does intellectual property law protect jokes?

Have you heard the one about Keith Chegwin standing accused of stealing gags?

The comedian has been attacked for supposedly posting other comics' material on his Twitter feed and passing it off as his own - a charge Chegwin strenuously denies.

His critics insist that he has violated a "gentleman's agreement" among the comedy fraternity not to pilfer each other's material, but would doing so also constitute a breach of the law?

Matthew Harris of intellectual property specialists Waterfront Solicitors say that, in theory, a joke can be copyrighted - but with shorter, snappier gags which rely on abstract ideas rather than specific plots, any infringement would be difficult to prove in an English court.

"The joke would have to be more than just a few words long," he says.

"As long as it's not word-for-word identical, there would have to be a relatively detailed plot [for it to breach copyright]. And if that plot were so abstract as to fall within the general field of comedic tools, that's fairly debatable.

"I think a one-liner would fall on the cusp of what's covered by the law."

In other words, he says, simply changing a long, detailed Englishman, Irishman and Scotsman joke to one with a Frenchman, a German and a Spaniard and an identical plot would not be enough to protect a plagiarist.

But the more succinct a gag and the more generic the basis of the humour - politicians being crooks or Manchester being rainy, say - the less likely that a court would rule that anyone could not have come up with the quip independently.

The Answer In theory, jokes can be copyrighted

But with shorter, generic, more abstract gags it is harder to prove infringement

If the jokes are sufficiently similar, the burden of proof passes to the defendant

However, Mr Harris adds that were the joke sufficiently similar to the one allegedly being plagiarised, the burden of proof would fall on the defendant rather than the complainant to demonstrate that he or she came up with the idea alone.

It is a highly complex legal conundrum, and it appears that, so far, jurisprudence has not reckoned with the likes of Keith Chegwin.

For his part, the comedian insists that he had come up with the jokes on his Twitter feed himself or "remembered [them] from old".

However, fellow gagsmiths insisted that one example - "My auntie Marge has been ill for so long we changed her name to 'I can't believe she's not better'" - was the work of Mock the Week's Milton Jones.

WHO, WHAT, WHY? A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines

Other tweets were said to have been pilfered from Jimmy Carr and The Simpsons, according to Chegwin's accusers, comedians Simon Evans and Ed Byrne.

Nor is the idea that the courts could get involved in such disputes entirely fanciful.

In 2004 Jimmy Carr issued legal threats to fellow comic Jim Davidson for using a similar joke to one of his own.

For what it's worth, the quip ran: "Someone came up to me last week and complained about a joke, quite a big-boned girl. She said: 'I think you're fattist.' I said: 'No, I think you're fattest.'"

It may sound trifling, but comedians whose livelihoods depend on making audiences laugh complain that such behaviour is no laughing matter.

The thing with jokes is that once audiences have heard them, they're no longer funny Dan Antopolski, Comedian

The comedian Dan Antopolski had to confront this dilemma after one of his one-liners won the best joke award at the 2009 Edinburgh Festival Fringe.

Soon after the gag - "Hedgehogs: why can't they just share the hedge?" - was given the accolade, it went viral across the internet.

But quickly, he realised he would have to drop the routine from his set - because his audiences had already heard it, and some might even assume that Antopolski had plagiarised the gag himself.

His agents were also forced to issue a cease and desist order to a company which produced T-shirts reproducing the joke.

"The thing with jokes is that once audiences have heard them, they're no longer funny," he says. "In my Edinburgh Festival comedy world, the ethic is that you write your own material.

"In the traditional Bernard Manning days, it was different because any two comedians might never play to the same audience. But TV changed all that.

"And now the internet means that people post up comedians' routines, and then they spread with no mention of who the author is - it's difficult to talk about it seriously because it all seems so silly, but this does affect people's ability to make a living."

Silliness may be what comedy is all about. But with the web making artists protect their intellectual property more fiercely than ever, such complaints are unlikely to be laughed out of court.