Scams can operate by junk mail, text message or telephone

The scams often start with letters, phone calls or text messages telling the recipient they have won a "prize".

In order to claim, however, the person has to call a premium-rate phone line or send cash to cover delivery.

The Trading Standards Institute (TSI) said the prize often does not exist or is nothing like the description.

The TSI wants the scope of the government's Gambling Bill to be extended to protect consumers over prize competitions of this kind.

It believes there should be a legal limit of �1 on how much consumers can be asked to pay in order to claim prizes.

"Bogus prize competitions are now probably the number one source of complaint to trading standards services across the UK," said TSI chief executive Ron Gainsford.

Teresa Perchard, policy director at Citizens Advice, said: "The best advice we can give is that people should not pay any money up front if they're told they have won a prize.

"It is easy to fall for such dodgy competitions - who wouldn't be excited by the prospect of a great prize?

"But so often there is not a prize and it's almost impossible to get your money back once you've paid out."