U.K. Defamation Acts 1952, 1996.
Defamation is a civil "common law" in respect of which the Defamation Acts of 1952 and 1996 provide certain defences. It applies to any published material that damages the reputation of an individual or an organisation, and it includes material published on the internet. A civil action for defamation can be brought by an individual or a company, but not by a public authority. It is up to the claimant to prove that the material is defamatory. However, the claimant does not have to prove that the material is false — the burden of proof on that point lies with the author/publisher, who has to prove that what they have written is true.
Where defamatory material is posted on a website the person affected can inform the host of its contents and ask the host to remove it. Once the host knows that the material is there and that it may be defamatory, it can no longer rely on the defence of innocent dissemination in the Defamation Act 1996. This means that the person affected could (if the material has been published in the jurisdiction, i.e. in England and Wales) obtain a court order (an injunction) to require removal of the material, and could sue either the host or the person who posted the material for defamation.