Comedians are fuming as their jokes are being plagiarised on Twitter and other websites.
Comics have complained that the reason some of their gags were falling flat was that many people in the audience had already read them online.
They claim that their stand-up routines are being pilfered by viewers who then reproduce their work online.
Legal experts have suggested that comedians should save their jokes on computer as soon as they write them and record the date to provide evidence to fight potential copyright cases.
An up-and-coming British comedian has raised the issue after becoming embroiled in a row with a comedy website.
Gary Delaney noticed that a number of his one-liners had been posted without attribution on Sickipedia.org, a huge online joke compendium. When he contacted the site and requested that they be taken down, he was subjected to a torrent of abuse at the hands of its users.
The comedian was first alerted to the situation when he noticed that crowds seemed to know what he was about to say, even while he was performing relatively recent material.
Delaney told the comedy website Chortle: “A couple of jokes, I can tell from the audience reaction, have very quickly started to get around.
“A joke I had... I could tell that sometimes the audience knew it before I did the punchline, when I hadn’t even been doing it that long.” Delaney also said that his work was being devalued by people posting his jokes on the micro-blogging site Twitter.
“If I post a joke on Twitter, I can’t get annoyed if people post that round because I’ve already done it on a public forum,” the Telegraph quoted him as saying.
“But the jokes from my club set are how I make my living, my best and biggest jokes. It used to be the case that a comic’s set would last decades. But now I’ve got jokes I wrote in May, June and July that aren’t working by October because they’ve been absolutely trashed around the Internet,” he added.