BEWARE THE BOGUS BANK EMPLOYEES WHO COULD SCAM YOU OF YOUR LIFE SAVINGS

Police are warning of 'courier fraud', where victims dial their bank's number and speak to 'staff' who persuade them to part with huge sums of money. It starts with a phone call from someone pretending to be from your bank, and can end with the loss of £40,000 or more. It is one of the most sophisticated bank frauds police have seen; one that targets older women in well-off areas. The banks know it is going on but are refusing to reimburse victims. So why have there been so few warnings about this scam? That is the question the family of Cecily Grange* were asking this week. The 76-year-old from Windsor lost £23,000 earlier this year after two conmen persuaded her they were calling from her local Barclays branch, and that she needed to move her savings to a "new account" that staff had supposedly set up. In a separate incident, Oxford woman Mary Wilson* lost £7,000 in similar circumstances. In her case, she handed the cash to a courier who arrived at her door. Wilson believed she was helping to track and capture bank staffs who were stealing customers' money, while Grange thought she was moving her savings to prevent fraud.

Both women were rung up out of the blue and told that their bank suspected they had been victims of fraud. They were invited to call the bank back, using the phone number on the back of their debit card. Having dialled the bank's number, the victims assumed they were speaking to bank staff; but in both cases the conmen had kept the line open. Many people are unaware that a phone line can remain open for up to five minutes after the handset has been put down by the person receiving the call, enabling fraudsters to stay on the line to impersonate a victim's bank. Police say scammers have refined "courier fraud" into a fine art. This month, City of London police revealed that 2,556 courier fraud offences were reported to the Metropolitan police between April 2013 and March 2014. This is a nationwide problem: since February, Greater Manchester police has recorded 346 offences, while in one of the cases investigated by Devon and Cornwall police, the victim lost £40,000.

In its simplest form, courier fraud is where scammers phone the victim, purporting to be from their bank, the police, or another law enforcement agency. They then dupe the person into withdrawing a large sum and handing it to a courier or taxi driver, who may not know they are being used as part of the scam. Often, the victim is asked to assist with a police investigation, or told there is a corrupt member of staff in the bank and asked for help to identify them. The victim is told the money will be "marked" and collected. They may be asked to ring the number on the back of their card, convincing them the call is genuine. In Grange's case, the caller rang her in February to say that someone had siphoned £1,000 out of her accounts and asked whether she had authorised the transactions. Greatly alarmed, she was persuaded she must immediately transfer her remaining balance into a new account that had been set up for her. Her family says she was not asked for her pin, and knew not to give it to anyone. The conmen were so convincing that they persuaded Grange – who suffers from poor health and requires a stick to go any distance – to walk from her flat to her Barclays branch in Windsor. There, she stuck to the line she had been given that she was not to discuss the matter with the cashiers, as they might be the fraudsters.

Grange's daughter, who contacted Guardian Money, has questioned why staff who, she says, would have been aware of the scam did nothing to stop her mother as she emptied her current and savings accounts and sent the total of £23,000 to a TSB account, an account into which she had never paid any money previously. Barclays has told her it is not liable for the losses. "I appreciate Barclays could well argue they have no obligation to reimburse my mother, as it was not a fraud involving a credit or debit card, nor did it involve a third party withdrawing funds from her account. However, she did so because she genuinely believed Barclays had instructed her to, and because she was too elderly and unwell to realise she was being duped," says Grange's daughter. Mary Wilson's case is similar. She was persuaded to withdraw £7,000 by fraudsters who rang her Oxford home at the end of January while her husband was on business. In her case she was told to take the money out of the couple's joint account in cash, and to hand it over to a courier, who would come to her home. Again, she was told not to answer any questions as to why she was taking out such a large sum. She was repeatedly reassured that once the sting had been enacted, her money; marked and followed by police would be returned, and that she was being a great help to the authorities. NatWest, her bank, has told her it will not refund her losses.

The figures, for London only, show the average age of a victim was aged 54, and nearly two thirds of victims were female. The average loss was around £2,600. Last week, the Met police launched a Courier Fraud Awareness Day, but failed to tell anyone. Guardian Money only came across it while researching this article. The campaign has been backed by Barclays and Natwest, as well as Santander. The Met police insist much has been done in the last year to tackle courier fraud, but adds that this crime "continues to evolve; we want people to question even truly genuine-sounding calls and, most importantly, remember police and banks will never ask for your pin or bank card, so you should never give these away."

A spokesman for Barclays says their staffs constantly try to strike a balance between honouring customers' wishes to withdraw their own money, and doing their utmost to prevent fraud. In Grange's case, staff identified her using chip and pin technology, and identification and verification checklist was completed, it says.

"Staffs are trained to be alert to unusually large transactions, but there are also situations in which a transaction appears unusual but the customer would like it to go ahead for valid reasons. Our guidance highlights key warning signs branch staff should look for, and encourages them to tactfully ask the customer why the transaction is required. At the time [we] concluded that the funds were required for a genuine purpose. Therefore we are unable to reimburse these funds," he says.

A spokeswoman for NatWest confirmed it will not refund Wilson as she had "willingly handed over the money". "We would advise all our customers to be extra vigilant and in the case of suspicious or unexpected calls, always verify the caller using an independently checked telephone number and using a different phone line."

These cases may help explain why – as reported by Money last month – HSBC has been asking some customers making large cash withdrawals to provide documentary evidence of what the money is needed for. At the time the bank said it was to "reduce the risk of money laundering, fraud and other crimes". Regulator Ofcom says it is working with the police and the telecoms industry to help stamp out courier fraud, and adds: "Over the past year a number of telephone providers have made changes to their networks to cut the time a phone line remains open to a couple of seconds. This has stopped fraudsters being able to stay on the line to impersonate a victim's bank or the police."

* Names have been changed