Websites such as Facebook and Twitter could be forced to unmask so-called internet trolls, under new government proposals in the Defamation Bill.

The bill, which is being debated in the House of Commons today, will allow victims of online abuse to discover the identity of their persecutors and bring a case against them. The move also aims to protect websites from threats of litigation for inadvertently displaying defamatory comments.

“As the law stands, individuals can be the subject of scurrilous rumour and allegation on the web with little meaningful remedy against the person responsible,” said Justice Secretary Ken Clarke.

“Website operators are in principle liable as publishers for everything that appears on their sites, even though the content is often determined by users. But most operators are not in a position to know whether the material posted is defamatory or not and very often – faced with a complaint – they will immediately remove material.

“Our proposed approach will mean that website operators have a defence against libel as long as they comply with a procedure to help identify the authors of allegedly defamatory material.”

Clarke added that the government wants a libel regime for the internet that makes it possible for people to protect their reputations online, but also ensures that information cannot be easily censored by casual threats of litigation against website operators.

“It will be very important to ensure that these measures do not inadvertently expose genuine whistleblowers, and we are committed to getting the detail right to minimise this risk.”

The move comes after a British woman won a landmark case to force Facebook to reveal the identities of internet trolls. On 30 May, Nicola Brookes from Brighton was granted a High Court order after receiving “vicious and depraved” taunts on Facebook.

In the first ruling of its kind, Facebook will be obliged to reveal the names, email and IP addresses of those behind the abusive messages, showing who they are and where they posted from. Brookes plans to bring a private prosecution against at least four of her persecutors.

Meanwhile, a man called Frank Zimmerman who sent a threatening email to a Conservative MP Louise Mench was banned last week from contacting a host of celebrities. Like Nicola Brookes' case, that of Louise Mench involved criminal harassment, not defamation, which is a civil matter.