A science writer who is being sued for libel by the British Chiropractic Association is to fight on after a preliminary judgment against him was opened up to appeal today.

Simon Singh was sued by the BCA after he wrote an article in the Guardian criticising the association for supporting members who claim that chiropractic treatments – which involve manipulation of the spine – can treat children's colic, sleeping and feeding problems, frequent ear infections, asthma and prolonged crying.

Singh described the treatments, for which he said there is no evidence, as "bogus" and criticised the BCA for "happily promoting" them.

In May, Mr Justice Eady in the high court ruled on the meaning of the words, saying they implied the association was being deliberately dishonest. Singh said that interpretation would make it difficult for him to defend himself at a full trial.

Singh was initially refused leave to appeal, but Eady's interpretation was deemed to be open to argument by Lord Justice Laws, who said Eady had risked swinging the balance of rights too far in favour of the right to reputation and against the right to free expression. It was arguable, he said, that Eady's judgment on what constituted comment had been wrong in law: "It is arguable that his approach to the issue of whether something that was objectively verifiable could be a comment was legally erroneous ... I give no finding as to the end result. I only give reasons why the appeal ought to be allowed to go forward. "

Many scientists and science writers have rallied to Singh's support, claiming that the freedom of scientific opinion is at stake.

Speaking after the judgment, Singh said this was the "best possible result".

"Simon Singh's battle in this libel case is not only a glaring example of how the law and its interpretation are stifling free expression, it shows how urgent the case for reform has become," said Jo Glanville, editor of Index on Censorship.

• This article was amended on 20 and 22 October 2009. The original reported Simon Singh's contested Guardian piece as having said there was "not a lot of evidence" for the claims made for certain chiropractic treatments. A heading said that the latest appeal court ruling had overturned the high court's preliminary judgment. The text also described the appeal court as having rejected the high court ruling and termed it "legally erroneous". This has been corrected.