People aged over 55 could be four times more likely than the general population to become victims of a telephone scam where fraudsters pose as a bank or the police, according to figures from the financial ombudsman.

The Financial Ombudsman Service (FOS) reviewed 185 phone scam cases involving "vishing" and "no hang up" frauds. It found that four out of five (80%) of the victims conned out of their cash were aged over 55 years old. One in five victims was aged over 75 years old.

The cases looked at involved total losses of up to £4.3 million. One in five (20%) people had lost between £20,000 and £49,999 and some victims had lost more than £100,000.

The ombudsman service is urging people visiting relatives over the summer to highlight the risks and help prevent such scams happening.

Vishing scams involve criminals tricking people out of their savings by pretending to be from a legitimate body such as their bank or the police. The no hang up scam is a type of vishing, where fraudsters persuade consumers that their account is at immediate risk and tell them that they need to move or withdraw their money urgently, using technical tricks on the phone line to add to the plausibility of the scam.

Sometimes, fraudsters stay on the phone line after speaking to the victim, so that when the victim puts the phone down and then tries to call their bank, they will still be speaking to the fraudster.

Most no hang up frauds seen by the ombudsman involve online money transfers, but some take place in branch. In some cases, people are tricked into giving away their Pin numbers over the phone and others give their card to a "courier" who then delivers it to the fraudster.

The ombudsman, which resolves disputes between consumers and financial firms, becomes involved in such cases when the victim does not think their bank has done enough to help them. In 37% of the cases looked at by the ombudsman, the complaint was upheld in the consumer's favour.

But the service said that banks have a duty to act on their customer's instructions - so if a consumer transfers or withdraws money themselves during a scam they are unlikely to get it back.

Caroline Abrahams, charity director at Age UK, said: " That anyone would target an older person to defraud them in the first place is abhorrent but we know that older people are deliberately targeted and can be especially at risk if they are living with dementia and/or cognitive decline.

"Some older people are more vulnerable to fraud because they live alone or in isolation, but fraud is something that can happen to any of us."

Last week, Financial Fraud Action (FFA UK) said that that £23.6 million was lost in 2014 across the UK due to victims being persuaded over the phone to transfer money from their bank account directly to fraudsters. FFA UK has teamed up with Neighbourhood Watch to issue warnings about phone scams.

July also marks Scams Awareness month and Citizens Advice and Trading Standards have teamed up to raise awareness of scams.

The ombudsman said people should never give out personal or banking information when answering an incoming call, and they should not rely on the caller ID for identification.

If someone has any doubts they should hang up and preferably use a different phone to call a trusted number.

Banks will never ask people for their full Pin numbers or ask them to key in their Pins into the phone keypad. They will never send someone to a customer's home to collect their bank card.

Caroline Wayman, chief ombudsman, said: "One of the most consistently challenging areas of our work is dealing with people who have been affected by financial fraud. These are extremely cruel and convincing deceptions and consumers are tricked into believing they are protecting their money, when in fact it is being stolen.

"Scammers are relying on people's vulnerability and vishing is particularly insidious in exploiting this. This is why 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 - stopping the fraudsters in their tracks."

Which? executive director Richard Lloyd said: "It is critical that banks act swiftly to help victims of scams and provide them with accurate information on their rights. With scams becoming much harder to spot and fraudsters using aggressive tactics to hook their victims, the old adage still stands - if something sounds too good to be true, it probably is.

"Our advice to consumers is to always check who you are dealing with before you hand over any cash and don't respond to unsolicited calls, texts or emails."