People who are the victims of so-called "vishing" scams cannot always rely on their bank to compensate them, a study has suggested.
In nearly two-thirds of cases the Financial Ombudsman Service (FOS) found that banks were not responsible for victims' losses.
It looked at 200 examples of the telephone fraud, in which account holders lost up to £100,000 each.
But it ruled that the bank was liable for those losses in only 37% of cases.
In 63% of them, consumers were left without compensation, having, in effect, given their own money away.
As a result it is warning that account holders need to be much more aware of the risks.
"We really want to share what we are seeing in the complaints we handle, and encourage people to get talking about scams with their friends and relatives so they become more alert to the risks," said Caroline Wayman, the chief ombudsman.
'No hang-up' scam
"Vishing" - or voice phishing - occurs when fraudsters phone up, posing as the police or the victim's bank. Last year the scam cost customers £24m, according to Financial Fraud Action.
Usually the fraudsters persuade their victims to move money from their account.
Often they do this by telling customers to phone their bank immediately. However the fraudster stays on the line, tricking the victim into thinking they are talking to their bank directly.
This is known as a "no hang up" scam.
How to protect yourself against vishing
Banks will never
- ask you to authorise a transfer of money to a new account, or hand over cash
- ask for your PIN or passwords in full on the phone or via email
- send someone to your home to collect cards or cash
- ask you to send personal banking information via email or text
- ask you to carry out a test transaction online
- call you to advise you buy diamonds, land or other commodities
The FOS found that 80% of consumers conned out of their cash were over the age of 55.
But it is a grey area for banks, who have also lost millions of pounds.
Some banks do pay compensation, while others do not.
"Every case is slightly different," said a spokesperson for the British Bankers Association.
"That's why banks look into the details of each case, rather than having a blanket policy for all instances of vishing," he said.