The policeman phoned your friend numerous times over the following days and warned him to tell no one about the operation. The scammer claimed the cash had been counterfeit and that someone had been arrested at Barclays as a result. The sting continued in this vein for several days, when your friend was then asked to use £30,000 in his account to buy gold bullion. The explanation given was that the gold company was also under suspicion.

This time the wife was instructed, on two separate occasions, to order some gold ingots from a genuine company called UK Bullion, with the husband making the payments by bank transfer at the Barclays branch. When the gold bars arrived at their home he wrapped them up, as he did with the banknotes, and the packages were collected by the same masked courier.

The crooks then got greedier and demanded his wife withdraw £15,000 from her Barclays account. When the couple arrived to collect the money the cashier questioned the wife about what it was for. At this point she broke down and went on to explain the whole chain of events. It was only then her husband realised he had been a victim of a ­terrible scam.

It is horrific to see honest people duped in this way. The fake police were so convincing that it is no wonder your friends fell for their tricks. By suggesting the husband call 999 he was reassured their claims were genuine. What he did not realise was that the scammer had not hung up the phone line, so that when he dialled the emergency number he was in fact simply put back through to the original scammer, who then pretended to be a different officer apparently corroborating the earlier claims.

Although these crooks demanded cash first, they then moved on to gold, a trend the police say is growing. This is because the yellow stuff is harder to trace than banknotes, making it increasingly popular with thieves and money launderers. In the past 13 months, there have been 3,293 courier scams reported with £14.5m stolen, according to the National Fraud Intelligence Bureau – likely to be an underestimate because many victims are too embarrassed to admit to having been hoodwinked.

I asked Barclays to reopen the case, feeling encouraged by some previous success with a case I came across in May of a woman conned out of £90,000 by fake police. After my intervention, her bank, Halifax, returned half her losses.

Barclays agreed to look again at what happened. A couple of weeks later my optimism was rewarded, as it responded with the excellent news that it would be returning your friends’ money after all. The incident did not fall under the Contingent Reimbursement Model Code, where banks will automatically refund victims of certain authorised push payment frauds, but Barclays chose to repay the money as a goodwill gesture.

It felt staff could have discussed scam prevention measures more and queried the purpose of the gold bullion purchase in more detail. For that reason it added £400 in compensation. Your friends were “over the moon”.

A Barclays spokesman said: “We have every sympathy with our customer, who was the victim of a unique and sophisticated courier scam, and have reimbursed him for the full amount that was lost from their account. We encourage customers to be vigilant, and to remember that the police will never ask you to withdraw money or hand over goods you have purchased as a result of a phone call.

“Our research found that a quarter of the public are likely to agree to assist in an ‘internal bank investigation’ – something we would never ask you to do.”