Scotland Yard faces a £1.3 million budget hole after a celebrated operation to seize uninsured vehicles fell short of expectations.
Operation Reclaim was launched across the capital after a law change enabled any officer to act on vehicles found without correct paperwork.
Senior staff said the scheme would cut crime, get unsightly and polluting vehicles off the streets and boost the force's coffers.
But new figures revealed police expect to seize 36,000 vehicles by April, 24,000 fewer than anticipated.
As a result, the Metropolitan Police is bracing for a £1.3 million shortfall from the £3.2 million in fines and fees it was expected to collect.
Nevertheless, the force said the operation has been a success with far higher numbers of vehicles removed than in previous years.
Jenny Jones, a member of the Metropolitan Police Authority (MPA) who campaigns on road safety, said more work needs to be done to tackle uninsured drivers.
She said: "Two decades of neglecting this issue have led to a culture of lawless roads where far too many motorists in London feel they can drive without insurance and get away with it.
"It is staggering to think that in parts of London one in four road collisions leading to an injury involves a hit-and-run driver.
"I think it is great that the police in most areas of London are finally getting on top of this problem.
"However, some borough police commanders are still not seeing the clear link between uninsured driving and main stream criminality."
News of the seizure shortfall will be a blow to senior police officers who invested £600,000 in new offices for backroom staff.
They also considered using two extra car pounds in north east and south west London to deal with thousands of vehicles.
Scotland Yard makes money from seized vehicles by charging owners £150 to reclaim them, plus £20 for every day they are stored.
The Motor Insurers Bureau estimated there are some 435,000 uninsured vehicles being used on London's roads, with numbers rising steadily.
The Metropolitan Police handed borough officers powers to seize uninsured cars, lorries and motorcycles after a change in the law in 2005.
The decision came after 3,000 vehicles were seized in one year during a pilot in Hounslow, compared with 10,000 across the rest of the force.
A Metropolitan Police spokesman said the number of vehicles seized for no insurance and other offences has risen from 12,000 in 2007-08.
She said: "By the end of this financial year, we anticipate we will have seized 36,000 uninsured vehicles.
"This will generate approx £2 million of income, disrupt crime and improve road safety. We consider this a success.
"The Met in conjunction with the MPA sets itself challenging targets, however this is still a fairly new initiative and we have had to revise these.
"Policing is dynamic and resources are allocated accordingly.
"For example, this year we have had the Tamil protests, G20 and climate camp all of which have required significant resourcing.
"We are committed to Operation Reclaim and we have invested in our facilities to cope with the significant increase in the number of vehicles seized.
"This includes increasing the space for storing the seized vehicles and improving counter facilities for dealing with the public."Reuse content