Science writer Simon Singh today won his Court of Appeal battle for the right to rely on the defence of fair comment in a libel action.
Mr Singh was accused of libel by the British Chiropractic Association (BCA) over an opinion piece he wrote in the Guardian in April 2008.
He suggested there was a lack of evidence for the claims some chiropractors make on treating certain childhood conditions including colic and asthma.
The BCA alleged that Singh, in effect, had accused its leaders of knowingly supporting bogus treatments.
In May last year, High Court judge Mr Justice Eady, in a preliminary ruling in the dispute, held that Mr Singh's comments were factual assertions rather than expressions of opinion - which meant he could not use the defence of fair comment.
Today, the Lord Chief Justice Lord Judge, Master of the Rolls Lord Neuberger and Lord Justice Sedley ruled the High Court judge had "erred in his approach" and allowed Mr Singh's appeal.
Mr Singh described the ruling as "brilliant", but added: "It is extraordinary this action has cost £200,000 to establish the meaning of a few words."
The Singh case has become a cause celebre for science journalism and prompted calls for reforms to the defamation law to keep it out of scientific disputes.
After today's ruling, Tracey Brown, spokeswoman for the Coalition for Libel Reform, said: "We are delighted with the judges' ruling, but it does not go far enough.
"There is a cardiologist currently being sued by a device manufacturer, we have researchers who have been unable to publish their critique of lie detector technology because of threats of libel action.
"A major science journal is also currently being sued and our academics are being told to pull down blogs.
"We urgently need a public interest defence so that we can all be sure of our rights as publishers, writers, authors and academics."
Handing down the unanimous judgment of the court, Lord Judge said Mr Singh's defence had set out the undisputed fact that the BCA promoted chiropractic as a treatment for infants and young children suffering from colic, sleeping and feeding problems, frequent ear infections, asthma and prolonged crying.
Mr Singh also set out, ailment by ailment and study by study, his reasons for considering that none of the available epidemiological evidence reliably supported the BCA claims.
The BCA contested his view - "again ailment by ailment and study by study" - and asserted that there was some dependable evidence for its claims.
Until Mr Justice Eady blocked it in the High Court, Mr Singh's primary defence to libel was that his were expressions of opinion and fair comment.
Lord Judge ruled that the High Court judge, "notwithstanding his very great experience", had erred by treating an issue of opinion "as an issue of verifiable fact".
Mr Singh's words, "however one represents or paraphrases their meaning, are, in our judgment, expressions of opinion".
He said: "The opinion may be mistaken, but to allow the party which has been denounced on the basis of it to compel its author to prove in court what he has asserted by way of argument is to invite the court to become an Orwellian ministry of truth."
Ruling that Mr Justice Eady had erred in his approach, Lord Judge said the court adopted what Judge Easterbrook, now Chief Judge of the US Seventh Circuit Court of Appeals, had said in a 1994 libel action over a scientific controversy.
Judge Easterbrook had declared that those claiming they had been libelled "cannot, by simply filing suit and crying 'character assassination!', silence those who hold divergent views, no matter how adverse those views may be to plaintiffs' interests.
"Scientific controversies must be settled by the methods of science rather than by the methods of litigation. More papers, more discussion, better data, and more satisfactory models - not larger awards of damages - mark the path towards superior understanding of the world around us."
Lord Judge said libel was an area of law sometimes concerned with "conflicting issues of great sensitivity involving both the protection of good reputation and the maintenance of the principles of free expression".
He said it was "somewhat alarming" to read in the standard textbook, The Law Of Libel And Slander, that the defence of fair comment was still "dogged by misleading terminology".
Calling for changes, Lord Judge said: "We question why this should be so. The law of defamation surely requires that language should not be used which obscures the true import of a defence to an action for damages."
Other countries, including New Zealand, Australia and the Republic of Ireland, now described the defence of fair comment as "honest opinion".
Lord Judge said describing the defence "for what it is would lend greater emphasis to its importance as an essential ingredient of the right to free expression".
"'Honest opinion' better reflects the realities. This appeal must be allowed."
Richard Brown, president of the British Chiropractic Association (BCA), said an appeal to the Supreme Court was now under consideration.
Mr Brown stressed: "It never was, and it is still not, our intention to curb freedom of speech, whether in the field of scientific research or elsewhere, although sadly we recognise that this is how it has been portrayed by Dr Singh and his supporters".
Dr Singh had made a serious attack on the reputation of the BCA and stated in print and online that it "happily promotes bogus treatments".
Mr Brown said: "We are, of course, disappointed to lose the appeal, but this is not the end of the road and we are considering whether to seek permission to appeal to the Supreme Court, and subsequently proceed to trial.
"Our original argument remains that our reputation has been damaged.
"To reiterate, the BCA brought this claim only to uphold its good name and protect its reputation, honesty and integrity".