Trading standards chiefs are warning residents to be wary of an offer which urges people to call a premium rate telephone number.

Thousands of letters have been sent to residents in Brighton and Hove, Worthing and West Sussex.

The letters are printed in red ink with the heading Important Official Notification and tell the householder they are guaranteed a prize if they call.

Recipients are told they are guaranteed a free gift, including a Sony television, luxury garden furniture, a £5,000 world cruise, a computer game console and a digital watch.

But closer inspection reveals the calls to the hotline cost £1 per minute and was "likely" to last for nine and a half minutes, working out at about £9.50 a call.

The small print also stated there was no limit to the number of digital watches the company, which has a PO box address in Dublin, would give away. The letter did not print the name of the company behind the offer, although it did say it was not open to employees of Mega Prizes, a firm not listed in the telephone book.

Patrick Bligh-Cheesman, head of trading standards at West Sussex County Council, said: "The recipients believe these letters state they are guaranteed to win one of the prizes. But the reality is that, upon spending £9 on a premium rate phone call, the likelihood could be they may receive a cheap quartz watch."