A total of 13 incidents have been reported across eight north and east London boroughs since August using the same method.

The victims all received a call from a man claiming to be from the fraud department of a bank - usually Barclays - and stating their account had been subject to fraudulent activity.

The man then said he needed to collect each victim's bankcard for analysis and sent a courier to their home address to pick it up. Couriers were told to take the cards to various different addresses.

This was followed a short time later by further phone calls demanding the PIN with threats often made if the information was not given. On one occasion the suspect told a woman he would rape her if she didn't help and also threatened a male victim would be shot.

In some cases the fraudsters were successful in going on to steal money from the victims' bank accounts.

Detective Constable Deveci, from Chingford police, is leading the investigation.

He says: "Although all the victims are Asian, we think the suspects are simply cold-calling people and trying their luck. They can sound convincing and have managed to persuade people to hand over their bankcards and PIN numbers. Please be aware this scam is being carried out across north and east London and don't be taken in.

"We are also appealing for courier companies to be on their guard and report any incidents to us as the services of genuine companies are being abused by these fraudsters."