to prove that what they wrote was true. This does make it a lot easier to sue for libel in the UK than elsewhere.
There has been a development in this area, known as "qualified privilege". This was the defence the Telegraph used when sued by George Galloway last year. They didn't attempt to prove their story was true, but that they reported it fairly and without malice, and that the story was in the public interest. This had been established as a defence in a case brought against The Times by Albert Reynolds, the former Irish PM. But the court decided the Telegraph hadn't been fair in its reporting, so found for Galloway (this is now being appealed). See eg
http://journalism.cf.ac.uk/2005/MAJS/sjojbp/galloway.htmThere are also laws about privacy, such as publication of medical treatment details, or photos taken of people on private property.
However, for leaked government documents, it's most likely to be the Official Secrets Act that's used. Although we do now have a Freedom of Information Act, the government can refuse to release anything related to national security - as the Downing Street Memo was. Katherine Gun was charged under this act when she revealed we had been bugging UNSC members before invading Iraq.
On the brink of war last March, The Observer obtained a top-secret email from the US National Security Agency asking spies at GCHQ to help carry out an illegal intelligence 'surge' on the UN Security Council. The memo asked for 'the whole gamut of information that could give US policymakers the edge in obtaining results favourable to US goals or to head off surprises'. The operation targeted Angola, Cameroon, Chile, Bulgaria, Guinea and, most controversially, Pakistan.
Gun, a 28-year-old Mandarin translator at GCHQ, was arrested for leaking the memo and charged with breaches of the Secrets Act eight months later. Her trial collapsed in February after her lawyers demanded disclosure of the Attorney-General's legal advice. The government said the trial was dropped because new intelligence had been received which revealed they would be unlikely to gain a conviction.
The Official Secrets Act prevents Gun from inciting others to breach Britain's tough secrecy legislation, but the documents concerned are not classified. The government has consistently argued that they are covered by conventions of legal confidentiality, which safeguard the relationship between lawyer and client.
At present there is no 'public interest' defence for whistleblowers unless they can argue that their leak was intended to prevent an immediate threat to life.
http://www.guardian.co.uk/freedom/Story/0,2763,1302631,00.htmlI wonder if her trial would have gone ahead if they had already been forced to publish the AG's advice on the Iraq invasion at that time.