Police are to crack down on bureaux de change and currency transfer businesses in London suspected of being used to launder drugs money – as part of a bid to stem the surge in street violence.
Scotland Yard says it has linked violence in the capital and other parts of the UK to disputes between gangs.
It believes targeting their cash will disrupt activities and reduce attacks.
Police say 12 foreign currency exchange firms will be raided on Tuesday, the first day of the week-long operation.
Another 39 are set to be visited by inspectors to check they are fully complying with the law.
According to investigators, cash from drug deals usually arrives in bags and holdalls before it is processed through the business to make it look as though it has come from a legitimate source.
About £100bn is laundered through the UK every year, but it is not known much goes through money service businesses.
The companies handle tens of billions of pounds each year, with about 9,000 companies in London representing about a fifth of the UK market.
‘Cash is king’
Detectives say that while the vast majority of these companies operating are legitimate, a “significant number” are involved in illegal activity.
The crackdown is being carried out by the Metropolitan Police, HM Revenue & Customs and the financial services watchdog, the Financial Conduct Authority.
Det Ch Supt Mick Gallagher, who is co-ordinating the operation, said there were a lot of electronic transactions involved in money laundering but that “cash is still king”.
“It doesn’t take too much of a leap of faith to understand the causal link between what goes on with young men stabbing each other, and some of the bigger serious and organised crime syndicates.
“The cash is the lifeblood of this. What we hope to do, if you choke off the ability to trade effectively, then you disrupt the network.”
Following a separate operation in 2011, police described the use of legitimate bureaux de change by money launderers as a “weak point”.
A number of people were convicted of offences linked to drug dealing or money laundering in a case that exposed a London firm’s links to organised crime networks from all over the UK.