More than 1,300 police officers are taking part in raids across the capital to confiscate cash from suspected criminals.
Teams are targeting gangs involved in drug dealing, trafficking and prostitution in Scotland Yard's biggest ever operation to specifically focus on criminals' finances.
Cash sniffer dogs are being used to uncover hidden money and a series of arrests are expected to be made.
Around 200 financial experts will try to calculate how much money has been made from illegal activities, so it can be confiscated, and there will also be moves to freeze suspects' assets so they cannot be hidden abroad.
Commander Steve Rodhouse said: "Money is the main motivation for many criminals, be they heads of organised criminal networks, gang members or street-level offenders.
"The money they make from crime earns them status in the eyes of associates; it funds more crime and, for some, pays for them to lead luxurious lifestyles they do not deserve.
"They make billions of pounds from crime every year and it is their countless victims who pay the price - both literally and in respect of the emotional, mental and physical impact on them.
"When we take away criminals' money, we take away a lot of their capability and motivation to commit crime. This is why we have over 1,300 officers all set on depriving criminals across London of their criminal proceeds."
The action, Operation Stimtone 2, follows part one of the crackdown that was staged in May this year. More than 158 people were arrested, and £2.4 million seized. Officers also confiscated a motor boat worth more than £25,000 and designer watches valued at £1 million.
Scotland Yard said that as of 11.30am on Wednesday, £280,400 had been seized, including more than £100,000 from one address in Essex. Three BMWs and two Mercedes were being taken from a business in Havering. So far 110 people have been arrested for offences linked to economic crime, including 45 for fraud.