The number of libel cases in which claimants say they have been defamed online has more than doubled in a year - and the growth of social media may be a cause of the surge, according to new research.
But the total number of defamation cases brought rose by only 4%, from 83 cases in the year ending May 31 last year to 86 in the 12 months to the end of this May, say the figures, drawn from legal information provider Sweet and Maxwell's Lawtel and Westlaw UK services.
Experts had predicted that there would be a dramatic jump in online defamation cases following the birth of social networking and micro-blogging sites such as Facebook and Twitter.
Barrister Korieh Duodu, a media specialist with law firm Addleshaw Goddard LLP, said: "Social media tools have over a billion users worldwide and are growing rapidly in popularity.
"Nevertheless, they can present a huge problem for individuals and corporates trying to protect their reputations from harmful user-generated content.
"People who find themselves damaged on social media sites can often find it time-consuming and difficult to have the offending material removed, because many platform providers do not accept responsibility for their users' content.
"Such is the speed at which information travels through social networks that one unchecked comment can spread into the mainstream media within minutes, which can cause irreparable damage to the subject who has been wronged."
Much material on the internet is written by non-professionals without any of the fact-checking in traditional media organisations, he said, adding: "There is certainly a need for greater accountability of the providers of user-generated content, a need to tighten the regulatory framework within which they operate.
"This ought to have been a focus of the proposed Defamation Bill currently being debated."
A further issue is that journalists increasingly use social media platforms as news sources, which in turn increases the risk that content which is defamatory or breaches someone's privacy rights could spiral into a national news story.
The figures also showed that there was a large drop - 59% - in the number of celebrities suing for defamation, down from 22 in 2009/10 to only nine in the past year.
The drop follows the trend that celebrities are increasingly relying on privacy law and High Court injunctions to block publication of potentially damaging stories.
Mr Duodu said: "With injunctions becoming ever more popular in recent years, many celebrities are now utilising them to prevent stories gaining wider traction in the media.
"The increased use of anonymity orders in privacy claims has enabled well-known individuals to prevent anything being published at all. This will in some cases prevent the need for the individual to sue for libel after the event."