The legal action that the British Chiropractic Association has brought against Simon Singh means that many in the blogosphere are trying to understand the complexities of English libel law. So here is a brief guide.
1. The "claimant" (in this case the BCA) will first need to show that they have been defamed. This is a common law test and it usually means that the claimant's reputation has suffered. A defamatory statement in permanent form is called a "libel" (in transient form, it is a "slander").
The BCA are tereby complaining that a direct (or implied) statement about the BCA by Simon Singh has had the effect of lowering their reputation (rather than say the reputation of the Chiropractic generally).
2. Once the claimant has established that the statement is defamatory, the onus then shifts to the "defendant" (here, Simon Singh). This "reverse burden" of proof means that English libel law is regarded as unfair to defendants and too advantageous to the claimant.
3. There are three common defences: privilege, fair comment, justification. The defence adopted will depend mainly on what the claimant says is the defamatory meaning of the alleged libel. It does not appear that the defence has been served yet.
4. In English civil litigation, the losing party at Court will usually pay the legal fees in full for both parties (cf. USA). So if this case does go to Court, then either Simon Singh or the BCA will have a very hefty legal bill. This costs risk is the genuinely scary feature of English libel litigation - the costs often dwalf any damages. The legal costs of a libel case can be up to a million poumds.
5. The combination of the reverse burden of proof with the terrifying costs risk has meant that English libel law has often been abused by bullies, crooks and charlatans to close down public debate: Jeffrey Archer, Jonathan Aitken, David Irving, Robert Maxwell, etc.
6. Most cases, however, do not get to court. Only a small percentage of claim forms end up with fixed trial dates. For example, a case can be withdrawn or settled.
In summary, the BCA have adopted an action which means that they want the English High Court to ban Simon Singh from saying something which they allege to be defamatory about them. They also want damages and their costs for bringing the case. I suspect that they are expecting Simon Singh to settle, so as to avoid the terrifying costs risk.