People are being warned after a number of people were tricked them into handing over their life savings.
Safer Neighbourhoods Teams across Redbridge are urging people to be wary of fraudsters who use courier firms to steal money.
In the past four weeks, seven incidents have been reported, with three people handing over money.
The fraud sees the gang telephoning the victim, who is usually elderly, and claiming to be someone from an authority, usually the police, bank or Serious Fraud Office.
They tell the victim that their bank account security has been compromised and their card must be collected.
To convince the victims of their legitimacy they instruct them to hang up and call back on a genuine number to check that they are who they say they are.
The victim dials the new number but the fraudster does not disconnect so, unknown to the victim, they are still speaking to a member of the gang.
Usually, the victim is told to to reveal their PIN by typing it in on their keypad as the fraudsters can tell which keys have been pressed.
The suspect then sends a courier or taxi driver to the victim's house to collect their bank card, which the suspect has instructed them to put into an envelope.
Then, the card is delivered to a co-conspirator and is used, with the PIN, to empty the victim's bank account.
Police Detective Superintendent Ellie O’Connor of Redbridge Police, said: “These unscrupulous people target the most vulnerable members of our communities and prey on their trusting nature. Please know that my officers will never ask anyone for their bank card or their PIN number.
“The effects of becoming a victim of this despicable crime run far deeper than a loss of cash.
"Please work with us to ensure that those you care for have the confidence to hang up on anyone mentioning their bank card PIN and save them the anguish of falling victim to thieves.“