Fraudsters are conning older people out of thousands of pounds by asking them to pay off a non-existent tax debt in iTunes vouchers.
HM Revenue and Customs says hundreds of people have fallen victim to a scam in which a fraudster makes a cold call and tells them they owe a significant amount in tax, and says it can be paid off by buying iTunes gift cards.
After purchasing the card, the victim reads off the number, which the fraudster either sells on or uses to purchase high value products.
HMRC has written to the chief executives of major retailers, asking them to tell staff about the scam so they can help protect customers.
Action Fraud said there has been 1,500 victims, mostly over the age of 65, with an average financial loss of £1,150 though some have lost much more.
Following a previous awareness campaign, there have been examples of supermarket staff warning customers they may be falling victim to a scam when they purchase hundreds of pounds of iTunes vouchers.
Angela MacDonald, HMRC's director general of customer service, said: "It's really reassuring to see reports of supermarket staff, off their own back, taking action to keep customers safe.
"Raising public awareness is the best safeguard against this vicious scam.
"Supermarket staff are often the last line of defence against these fraudsters.
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"That's why I've written to the chief executives of major UK retailers to urge them to make their staff aware of this scam so they can help protect unsuspecting customers."
HMRC is also tracking down websites being used by the criminals and "initiating their takedown".