Back on topic, according to the McCann's English libel lawyers Carter Ruck...
There are three main defences available to a defendant in a libel action; namely, justification, fair comment and privilege.
1) Justification
The defence of justification, or truth, is a complete defence to a libel action. The onus is on the defendant to prove that the allegations are true.
Whilst the defendant does not, necessarily, have to prove the truth of each and every fact, he does have to prove the truth of the substance of the allegation, the defamatory 'sting'.
Even if a defendant is unable or unwilling to prove that the allegations are substantially true, he may nonetheless be able to defend the claim if he can show that it was fair comment or protected by privilege.
2) Honest comment
The defence of honest comment (formerly known as 'fair comment' until the Supreme Court judgment of Joseph v Spiller [2010] UKSC 53) applies only to expressions of opinion, rather than to statements of fact.
A restaurant or theatre review is a classic example of a publication which may be protected by honest comment, although this defence may apply in a variety of different situations.
To succeed in the defence of honest comment the defendant must show that the comment:
* is on a matter of public interest;
* is recognisable as comment, as distinct from an allegation of fact;
* is based on facts which are true (or protected by the defence of privilege);
* is on a matter which has been expressly or implicitly put before the public for judgment, or is otherwise on a matter with * * which the public has a legitimate concern; and
* must explicitly or implicitly indicate, at least in general terms, the facts on which it is based (i.e. what it is that has led the commentator to make the comment). Previously, the facts had to be identified sufficiently so as to enable the reader to judge for himself how far the comment was well founded, but following Joseph v Spiller this is no longer the case.
If the claimant can show that the comment was actuated by malice (meaning that the defendant was not expressing his genuine opinion) the defence of honest comment will be defeated. It is not enough, however, to show that the comment was prejudiced, exaggerated or 'unfair' so in practice it can be difficult to prove that the commentator acted 'maliciously'.
www.carter-ruck.com/Media%20Law/Questions_And_Answers.asp