A woman was recently conned out of nearly £20,000 by someone claiming to be from RBS. The victim, from Crocketford in Dumfries and Galloway, was phoned and told someone tried to withdraw £5000 from her account.
She was asked to confirm bank details and when she refused the caller told her to phone the bank to confirm the call was genuine.
But the original caller did not hang up, meaning that when the woman dialled for the bank she was still connected to the scam call.
The dedicated cheque and plastic crime unit, a police body that tackles UK financial fraud, calls such scams "courier fraud" as the caller often tells the victim the bank is sending someone to collect their card once they have obtained the details.
Strathclyde, Surrey and London are the worst-affected areas, while this type of phone scam is said to be increasing in the Grampian area.
Figures from the UK Cards Association and Financial Fraud Action show the scam has resulted in £7.5 million-worth of fraud in the UK between January and August.
Detective Chief Inspector Dave Carter, who heads the card crime unit, said: "There's been an exponential rise in reported case of this fraud. It relies on deception of the customer who, cases show, are often elderly and vulnerable, sometimes alone in the house and who often takes the fraudster's word at face-value."
Banks will never ask customers for pin numbers.