Letters offering prizes from a watch to a Mercedes car are dropping on doorsteps all over Oxfordshire.

But trading standards watchdogs warned householders to watch out for the elaborate phone-in prize giveaway.

The county has been inundated with letters from Budapest and Bratislava telling people they have won a prize.

To claim, entrants have to call a premium rate telephone number for up to nine minutes at £1 a minute - and the vast majority of prizes are expensive mobile phone contracts.

Trading standards officers believe the company behind the deal - which is promoted by Prize Group, of 10 Stratton Street, Mayfair, London - receives a percentage of the cost of each call.

The county's chief officer David Sibbert said: "We would recommend consumers should think carefully before responding to the promotion. You could find yourself landed with a hefty bill.

"We have heard of one elderly gentleman who was kept on the phone for 15 minutes and at the end he was offered a mobile phone. To qualify for it, he would have had to agree to an expensive year-long air-time contract.

"Sadly, the saying 'You don't get something for nothing' is still true." This is the second case in a few days highlighted by trading standards. In a separate inquiry, police are looking into an alleged £100,000 fraud involving Christmas hampers.

Thousands of people applying for the £99 hampers were urged to cancel payments amid questions over the legality of the offer by ACS Ltd, of 82 Great Eastern Street, London.

Oxfordshire applicants sent cheques after seeing the offer advertised last month for discounted hampers to be delivered to their homes. Two men from Guildford, Surrey, have been arrested and bailed by police.

In the latest case, one letter sent to residents states that calls will cost £1 a minute to claim a gift. So potential enquirers are being urged by trading standards to read the small print before responding.

A mum-of-two from Witney said two members of her family and a friend had received letters but spotted the potential hazard.

She said: "There are people who will make the phone calls and it will be the ones that can least afford the £9 call.

"It is the people with children who are hard up it will hit."

Trading standards watchdog Debbie Dent added: "The vast majority of people end up getting a mobile phone deal. You get a mobile phone but it does not end there - you have to sign up to a very expensive air-time agreement."

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