Conmen posing as police have been calling elderly people and asking them to withdraw large cash sums to be checked to see if it is counterfeit.
Taxi drivers in Hampshire have foiled two attempts to scam women in their 80s out of thousands by chatting to them while taking them to the bank.
Both attempted frauds of around £5,000 took place in the Bordon area, on Monday and Thursday afternoons.
Neither victim lost any money thanks to their vigilant drivers.
Det Con Jo Martindale, from Basingstoke CID, urged people to "keep an eye out" for elderly relatives and neighbours.
"Thankfully these two incidents were reported to police by taxi drivers," he said.
"Without this intervention the victims could have parted with large sums of money."
He said the police would never ask for bank details or cash to be given to them.