Major reforms of the libel laws will see a duty placed on internet service providers to try to identify internet trolls without victims needing to resort to costly legal action.

Websites will also be given greater protection from being sued if they help to identify those posting defamatory messages, under government plans.

The defamation bill, which will be debated in the Commons on Tuesday, will also see would-be claimants having to show they have suffered serious harm to their reputations, or are likely to do so, before they can take a defamation case forward.

The justice secretary, Kenneth Clarke, said: "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.

"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."

He added: "The government wants a libel regime for the internet that makes it possible for people to protect their reputations effectively but also ensures that information online can't 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 debate comes after an internet troll who sent a threatening email to a Conservative MP was banned last week from contacting a host of celebrities.

Frank Zimmerman narrowly escaped jail when a district judge suspended a 26-week prison sentence for two years after he sent an offensive email to the Corby MP, Louise Mensch.

The bill will also introduce a single-publication rule, so that the one-year limitation period in which a libel action can be brought would run from the date of the first publication of material, even if the same article is subsequently published on a website on a later date.

The reform is intended to end the situation by which material in online archives is regarded as being republished every time it is downloaded which, in effect, leaves the archive operator with a limitless risk of being sued.

The bill will also replace the common law defences of justification and honest comment with new statutory defences of truth and honest opinion.

The so-called Reynolds defence of responsible journalism published in the public interest also gets statutory recognition as responsible publication on a matter of public interest.