The Advertising Standards Authority (ASA) received 270 complaints about the West Yorkshire-based group's adverts.

They objected to the use of the phrase "final reminder" in bold red lettering.

The ASA told Damart to ensure this method was not used again. Damart said it had learned a "valuable lesson" and would not repeat the mailing.

The offending advert stated: "Having studied your account file, and unless our letters have crossed in the post, it seems that you still have available to you a number of offers that you have not yet taken up."

False impression

People who objected to the advert - many of them elderly - said it was "defamatory" because it gave the impression they owed payment arrears, the ASA said.

The mailing did not make clear that it was marketing material, the ASA found after investigating the complaints.

"The authority concluded that the mailing was misleading and distressing," the industry watchdog added.

Damart marketing director John Bottomley said: "We're really sorry that this letter has upset some of our customers.

"It is not in our best interests to cause them any distress and we would never knowingly set out to do so."

The company has apologised to offended customers by telephone, letter and via television interviews and has since reviewed its direct mailing procedures.