This follows three recent reports where a caller has pretended to be a police officer querying fraudulent transactions on bank accounts.
The caller has then asked for bank details, claiming that this will prevent further fraudulent transactions.
In one incident, a woman was duped into handing over some gold jewellery (pictured) to an unknown male.
He attended her house in Eccleshill in Bradford on 23 April after she told the caller she was afraid to keep it in the house after a burglary three years ago.
He is described as Asian and is believed to be in his late twenties, about 5ft 8ins tall and of slim build.
He had a short beard, short black hair and was wearing a black hooded top and blue tracksuit bottoms.
No money was handed over in the other incidents.
PC Toni Hinnells, of Bradford District CID, said:
“The police would never ask someone for their banking details or call to speak about suspected fraudulent activity on their bank account.
“If you receive one of these calls please hang up and contact your bank separately. They should be able to confirm if they are aware of any suspected fraud with your account.
“We would also advise that any personal banking documentation is shredded before being thrown away, as this will help to reduce the risk of being contacted by scammers.”
Any suspicious calls should be reported to Action Fraud on 0300 1232040.