Cases of cash machine fraud, where a device is used to trap money inside the ATM machine, have increased more than 15 fold in London in three months.
Reported incidents have risen from 150 across the UK in May, to 2,500 in London alone in August, according to figures from Link and London's Dedicated Cheque and Plastic Crime Unit (DCPCU).
Police said the scam spread as far as mainland Europe, but have become alerted to an increasing number of cases in the capital this April.
How the scam works
Det Ch Insp Dave Carter, head of the DCPCU, explained how this type of fraud works. "The criminal comes along and inserts a device called a cash claw into the cash point machine. They take a transaction of money out to enable them to put the device in," he said.
"They then leave it - it's undetectable, it's behind the guard on the cash drawer in the machine. Then the unsuspecting member of the public comes along, attempts to take some cash out.
"The money then gets trapped by this device in the cash drawer and then prevents them from taking the money out of the machine," he added.
"The machine goes out of service and then the criminal comes along, forces open the drawer using a pair of pliers or a screwdriver, forces the device out of the cash machine, bringing the customer's money with it."
Customers are reminded that they should immediately report any banknotes undelivered from cash machines.
Read more about the scam on the BBC website.
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To report a fraud, call Action Fraud on 0300 123 2040 or use our online fraud reporting tool.