Officers from Wiltshire Police said the con involved land lines and mobile phones and began with a recorded message.

The message said: "Congratulations, we are calling to advise you that you have won an all expenses paid trip to [and then a location]. Please press nine now to hear further details."

Police believed that if the recipient pressed nine and connected - even if they disconnected immediately - the other end would stay connected for a minimum of five minutes, at a cost of �100.

'Phone bill'

But, on Monday, it emerged that the email which generated the original warning of the scam was itself, phoney.

A message on the website of ICSTIS, the committee supervising standards of telephone information services, read: "A �20 per minute premium rate tariff does not exist.

"The highest premium rate tariff available is �1.50 per minute. Despite the hundreds of enquiries received by ICSTIS about this "scam" - and most have heard about it second or third-hand - not one person has been able to produce a phone bill to support their story.

"ICSTIS urges any individual or organisation that receives an e-mail about this scam to delete it immediately. Please do not forward it on to others."