Police have revealed that more than half a million pounds has been demanded from hundreds of people across the South West in "courier" frauds.
Devon and Cornwall police have revealed there have been 90 incidents in the region where one victim lost £40,000 to the scam.
The vast majority of victims are elderly, some of whom have been duped out of tens of thousands of pounds.
In Avon and Somerset, where 15 offences have been recorded, a victim lost £34,000 while in Dorset another was conned out of £28,000.
In all more than 200 offences have been recorded across the five forces in the South West.
The regional organised crime unit – Zephyr – is today rolling out a high profile publicity campaign to warn people about the threat.
Detective Chief Inspector Will White said: "We really don't know the extent of this extremely worrying problem.
"It is possible that the thousands of pounds which have been demanded and lost and the sums that we have been prevented from being surrendered may only be the tip of the iceberg.
Similar approaches have been used by the fraudsters across the South West and in other parts of the country. It started in the south east of England but has spread to other parts of the UK.
Conmen contact potential victims – who are normally elderly – by telephone. They are then encouraged, using an elaborate and convincing story, to withdraw large sums of cash, which they are then asked to send to London by taxi or courier.
The offenders often claim the money is potential evidence for an investigation and is required so that it can be forensically examined.
Avon and Somerset Police have arrested two men from London in connection with courier fraud and have been released on police bail, pending further inquiries.
Detective Chief Inspector Will White added: "It is possible that some victims may feel too embarrassed, ashamed or humiliated to come forward and report that they have been duped.
"We would like to hear from these people, so that we can establish how widespread this particular crime is and so that support and advice can be provided."
