Five sets of number plates were stolen across Barnet Thursday night in the latest of a string of similar crimes.
The thefts took place in areas including Edgware and Finchley and Barnet police believe the stolen plates are being used to conceal stolen cars or to run up parking and congestion zone fines.
It is thought that Barnet is particularly badly affected because it can be entered without paying the congestion charge.
Police believe that people drive into Barnet and then steal number plates so that they can enter the congestion zone without being accurately identified, and, therefore, without having to pay.
Police are advising drivers to fit tamper-proof screws to their number plates to avoid becoming a victim of this crime.
Anyone who has their number plates stolen should inform the police and the DVLA immediately.