UK libel laws work exactly opposite to those in most other countries. In this case, Singh said that chiropractic was bogus, and is getting sued by the BCA.
Now, in any sane country, the BCA would have to prove that
A - BCA has to prove that Singh is wrong and and chiropractic is perfectly supported
B - BCA has to prove that That Singh's statement caused damage.
But, in with the UK's libel laws, you're basically guilty until proven innocent. In this case, when the BCA sued Singh, Singh has to prove either
A - Singh has to prove that his statement was true
B - Singh has to prove no damage was caused.
Now, again, in a sane country, both A and B are impossible, the BCA would lose the lawsuit without Singh even getting a lawyer. But, in the UK, Singh needs his lawyers badly, because damage was caused, his only chance to win is to show that chiropractic is crap. A piece of cake if you're in a room with scientists, but when you're surrounded by lawyers and convincing a judge, it's not so east.