Twenty people have been arrested - and cars worth nearly £1 million seized - as part of police investigations into insurance scams and money laundering through an international hire car ruse.
Detectives in London carried out dawn raids after investigators said rental bosses were supplying criminals with incorrectly-insured cars to help them evade detection.
The Met Police's central criminal finances team gathered intelligence on a number of organised crime groups believed to be using the proceeds of crime to buy cars which they hired out to other criminals.
Police said the groups are suspected of exploiting weaknesses in insurance regulation by buying fleet insurance - cover for company cars which is much cheaper than hire insurance and means that no one person is associated with the car. This means the vehicle is much less likely to be stopped than a stolen or uninsured vehicle.
Officers said criminals are also laundering hundreds of thousands of pounds by claiming to take cash payments for hire when really the money is proceeds from other crime.
Detective Superintendent Nick Downing said: "These criminals are essentially using car hire firms to clean their dirty cash while simultaneously helping other criminals evade detection as they travel across London. They are doing this by defrauding insurance companies and, in doing so, they are also putting other road users at risk.
"This is just the start of this operation. As we continue to investigate other car hire firms, I encourage anyone with information about this type of crime to report it."
Around £25,000 in cash has been seized as warrants were carried out at 13 residential addresses and five businesses across London.
Four specific car hire companies were targeted and 14 people were arrested for money laundering, insurance fraud, possession of cocaine and immigration offences in Hounslow, Barking, Lambeth and Essex.
A further six arrests were made during a traffic operation which ran across London for seven days, starting last week. Automatic number plate recognition technology was used to stop cars flagged as being associated with a number of car hire companies under investigation. The arrests were for drug offences, drink-driving, breach of Asbo and fraud.
A total of 19 cars, worth around £950,000 as new, were seized for being incorrectly insured.
Anyone with information about money laundering or insurance fraud through car hire firms is urged to contact Crimestoppers anonymously by calling 0800 555 111.