Swiss firm Novachannel AG has written to a number of GPs telling them they are to be included in its Physicians and Therapists Guide.
The letter asks them to use the enclosed pre-paid envelope to confirm their personal details. 'By doing so you will be helping to keep the Medical Directory up to date,' the letter reads.
But the small print makes clear that those who reply are agreeing to have an advert placed in the publication, and will be billed for several hundred pounds.
Those who refuse to pay have been faced with a succession of letters threatening legal action, each demanding more money than the last.
A number of LMCs have warned their members to be wary of Novachannel and its various sister companies, including the European City Guide.
Dr Peter Graves, Bedfordshire LMC chairman, said the committee had put out a notice on its mailing list after one practice wrote in to say it had been caught out.
The various guides have tar-geted GPs since 2005, ostensibly because they have money but little time to read the small print.
Jules Woodell, who runs the 'Stop The European City Guide' website, estimates that they have earned their bosses over £50m over the last decade.
He added that only a fifth of those who have received demands for money have paid up.
'As far as we know, no one in the UK has ever been taken to court,' he said. 'The legal advice we've received is that, if you believe you have been deceived, you are within your rights not to pay.'
The international debt collection companies the group employs are in fact subsidiaries of the same holding company, he added.
The European City Guide has received large fines for misleading advertising in both Spain and Belgium.
The company could not be reached for comment, with emails and calls going unan-swered.
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