As the British Chiropractic Association's battle with Simon Singh continues to work its way through the legal system, chiropractors are counting the financial costs of a major backlash resulting from a libel action that has left the Lord Chief Justice "baffled". What was originally a dispute between the BCA and one science writer over free speech has become a brutally effective campaign to reform an entire industry.

A staggering one in four chiropractors in Britain are now under investigation for allegedly making misleading claims in advertisements, according to figures from the General Chiropractic Council.

The council, which is responsible for regulating the profession and has 2,400 chiropractors on its books, informs me that it has had to recruit six new members of staff to deal with a fifteenfold increase in complaints against its members – from 40 a year to 600. While it declined to comment directly on the costs inflicted by the reaction to the BCA's actions, it is clear that a six-figure sum will be involved for the extra staffing costs alone, to which will have to be added the considerable costs of any misconduct hearings.

The complaints all stem from a regulatory quirk exposed by blogger Alan Henness, who noticed that the council's rules demand that chiropractors do not make claims that conflict with past rulings by the Advertising Standards Authority. The advertising watchdog had previously criticised a number of chiropractors for making claims that their procedures can treat a variety of conditions, ranging from learning difficulties to arthritis.

The policy was exploited by numerous campaigners, who collectively worked their way through the BCA's membership list, Googling each member, and cross-referencing any claims on their website against previous rulings by the advertising watchdog. In a matter of weeks, complaints against more than 600 chiropractors had been lodged.

To the likely embarrassment of the BCA, those being investigated include its own officers.

While professional associations are remaining silent on the issue, at least in public, leaked e-mails reveal the scale of the panic the campaign has caused within the industry. Last June, the McTimoney Chiropractic Association issued an extraordinary plea to its 800 members, responding to, "what we consider to be a witch hunt against chiropractors":

"If you have a website, take it down NOW. "REMOVE all the blue MCA [McTimoney Chiropractic Association] patient information leaflets, or any patient information leaflets of your own that state you treat whiplash, colic or other childhood problems in your clinic or at any other site where they might be displayed with your contact details on them. DO NOT USE them until further notice."

Privately, a number of chiropractors have expressed unhappiness at the way the BCA, General Chiropractic Council and other professional associations have carried themselves over the past year, and lay the blame for the crisis firmly at their doors. In communications with me they have said the organisations' attempts to "medicalise" a form of alternative medicine have backfired. One remarked: "I am sure when the dust settles the BCA will lose a lot of members [...] Suing Simon was worse than any Streisand effect and chiropractors know it and can do nothing about it."

Further criticism has been focused on the BCA's presentation of supporting data, in particular its claim that a "plethora" of evidence backs the effectiveness of chiropractic in treating various childhood illnesses. Last year, facing demands that the BCA engage in scientific debate over its position, the association released its "plethora" to the public.

The statement, supported by just 29 citations, was ripped apart by bloggers within 24 hours of publication, before being subjected to a further shredding in the British Medical Journal. It emerged that 10 of the papers cited had nothing to do with chiropractic treatment, and several weren't even studies. The remainder consisted of a small collection of poor-quality trials.

More seriously, the BCA misled the public with a misrepresentation of one paper, a Cochrane review looking at the effectiveness of various treatments for bed-wetting, claiming that the authors had simply concluded that, "there was weak evidence to support the use of [chiropractic]."

In fact the quote in full reads as follows:

"There was weak evidence to support the use of hypnosis, psychotherapy, acupuncture and chiropractic but it was provided in each case by single small trials, some of dubious methodological rigour."

Now even the General Chiropractic Council has disowned the claims of the BCA – the same claims that lie at the centre of its libel action against Simon Singh.

In a new report, it has attempted to clarify the assertions that chiropractors can and cannot make, backed up by a systematic review of the evidence. Notably, the report concludes that the evidence does not support claims that chiropractic treatment is effective for childhood colic, bed-wetting, ear infections or asthma, the very claims that Singh was sued for describing as "bogus".

Whatever the eventual outcome of the BCA's legal action against Singh – and I would urge you to support science writers like Simon by signing the online petition for libel reform – one thing is clear. In pursuing a popular writer through the courts, it has inflicted a huge financial burden not just on its own coffers, but on those of the entire industry.

It is a lesson that other professional associations would do well to learn from in the future.

Martin Robbins writes for The Lay Scientist