Elderly and vulnerable residents in Bexley, Bromley, Lewisham and Greenwich are being warned against falling victim to courier fraud.
Between April 2013 and March 2014, 142 offences were reported to police in Bromley alone.
The figure was 80 for Lewisham, 73 for Bexley and 72 for Greenwich.
This is out of a total of 2556 similar offences reported to the Met over the same period.
The average loss to victims of sucessful scams was £2600.
Bromley is also the fourth worst hit borough in London since the start of 2014, with 47 offences recorded.
Courier fraud involves scammers telephoning the victim purporting to be someone from their bank or the police before duping them into revealing their PIN and handing over their card to a courier or taxi driver.
The victim may be asked to ring the number on the back of their card but the scammer keeps the line open so the victim unknowingly talks to another member of the gang, posing as a bank employee.
Met A/DCI Gary Miles said: "It is vital that people stay vigilant."