Six big City law firms are under police investigation for deliberately laundering money for organised crime, a leading detective has exclusively revealed to The Lawyer.

The firms are actively working as fronts for Colombian drugs cartels and organised crime syndicates in Eastern Europe, Italy and the US, as well as British gang, it was claimed.

The profits from drug trafficking, gun running and contract killings are being laundered by London lawyers, who set up offshore accounts and complex financial arrangements to disguise the money's origins, said Detective Chief Inspector Simon Goddard, of the National Criminal Intelligence Service (NCIS).

The capital has developed into an international centre for money laundering as a result.

Goddard, head of the organised and economic crime unit, told The Lawyer: “We know who they are. There are half a dozen, allegedly respectable, big city of London law firms that are actually working on behalf of organised crime.”

He refused to name the firms under suspicion, but added: “We are aware of some of their activities and we are at varying stages of our investigation. We certainly have lawyers who perform the role like an old consigliere in the Mafia films.

“They know who their clients are and know how their clients make their money and know it isn't from a legitimate activity.”

Solicitors are used to set up off-shore companies. Money is transferred by wire from its country of origin and deposited in a London account by the lawyer for a short time – giving it legitimacy – before moving it on to private accounts, explained Goddard.

He added: “In many, many cases the lawyer is the first person the organised criminal will go to to assist him in setting up money-laundering systems. The bottom line is if the lawyers were more honest, more diligent, then we would not have the problems that we are having.”

Goddard issued a warning to the firms under investigation: “They will be prosecuted for the same conduct as organised crime. We don't make any distinction at all.

The whole ethos of UK law enforcement is to not only arrest the principals in organised crime, but to seize their assets – and anybody trying to prevent law enforcement from seizing those assets is in trouble.

“This money represents heroin and other hard drugs on the streets of London. It represents vice money. Without the professional money launderers, our efforts to combat these crimes would be so much more successful.”

The Financial Action Task Force, an inter-governmental body set up in 1989 to combat money-laundering, met in London last week to discuss the problem.

“Most of the scenarios that were discussed over the two days involved lawyers being used to set up money-laundering systems on behalf of organised crime.

“It is not just the UK. It is a world-wide thing,” said Goddard.