The cynical con-artists are posing as the detectives working to bring them to justice, persuading their victims that they can help in a crime-fighting operation if they hand over cash or valuables.
And while the sophisticated racket has been seen across the country for some time, it has now begun targeting people in North and West Yorkshire.
Detective Inspector Jonathan Rowland, of North Yorkshire Police’s Economic Crime Unit, said there had been seven cases across North Yorkshire in the past two weeks and they suspected the fraudsters would continue to target the area in the weeks to come.
He said colleagues at West Yorkshire Police had also seen two similar cases in recent weeks.
He said the scam was “a well-worn path” which had been seen in other parts of the country before, but had never been seen to this extent in North Yorkshire.
He said: “I do not believe that it is people from North Yorkshire. I would expect this to be a national team of fraudsters.
“Wherever they are based, I don’t know, but they seem to be hitting us at the moment.”
The fraud often involves an unsolicited telephone call from someone claiming to be a detective at New Scotland Yard or an anti-fraud worker at a high-street bank, claiming to be investigating suspicious activity in the householder’s account.
Sometimes, they tell their target to hang up the phone and call 999 but unbeknownst to the victim, the team of fraudsters remain on the line and pretend to be police officers answering the phone.
The victim is often told that he or she could help to thwart fraudsters by moving money into a different account or handing over cash or valuables to a courier.
He said: “They are sophisticated. It is nasty because it can take people’s life savings.”
In a case in York last week, a woman in her 70s was persuaded to buy a Rolex watch and hand it over, with cash, to a courier. In total, she was conned out of £40,000. In another case, in Harrogate, suspicious bank staff alerted the police when a woman in her 80s asked to withdraw £17,000. Det Insp Rowland said luckily, this meant the woman did not lose her money.
He said: “People are falling victim to this type of fraud because they want to help the police. It is playing on people’s public-spirited nature. They want to help the police because they trust the police.”
He said the fraudsters often targeted elderly people and if they judged someone to be particularly trusting or vulnerable, they would attempt to take larger sums from them.
Det Insp Rowland said North Yorkshire Police was working with Action Fraud and other police forces to establish how many cases were believed to be linked.
People can protect themselves from falling victim to the scam by following police advice.
Det Insp Rowland said: “The police will never ask you to move money and will never ask you to be part of a police operation.”
He said if anyone received a suspicious call, his advice was to hang up the phone and not to make any outgoing calls for a few minutes, in case the caller was still on the line.
Anyone who has been a victim of fraud should call police on 101 or report it to Action Fraud by visiting actionfraud.police.uk or by calling 0300 123 2040.
Det Insp Rowland said victims were often too embarrassed to come forward but urged them to do so.
The warning comes in the same week that the boss of North Yorkshire’s multi-agency group to tackle scams against vulnerable people outlined the “massive challenge” facing the county, with its large and rapidly rising number of elderly residents.
Ruth Andrews, of the North Yorkshire County Council team, said loneliness often made people more vulnerable to scams as they were sometimes desperate for someone to talk to.