Following police raids across Canary Wharf, the City and Westminster five men from the self-proclaimed “Wolfs of Liverpool Street” (sic) were arrested on Thursday on suspicion of conspiracy to commit fraud by false representation and money laundering.

The raids were part of a joint operation between City of London Police and Action Fraud targeting groups that are cold-calling people purporting to have shares that promise high returns - yet in reality the shares are either worthless or non-existent.

Det Chief Inspector Dave Manley, who is heading up Operation Broadway, said: “In recent months we are finding evidence of boiler rooms creeping back into the City. This could be partly a result of the success we’ve had in shutting down these types of operations overseas and partly down to the fact that having a fancy office in the Square Mile makes it easier for the gangs to recruit.

“The City of London Police will not tolerate their existence and is committed to acting quickly to limit the harm they can cause to investors, especially the elderly and vulnerable, living across the UK."

DCI Manley said the scams often involve alternative investments that the Financial Conduct Authority would not be focusing on.

"You are looking at the sales tactics, the people they are actually, they are picking on the vulnerable, or on each occasions our victims are primarily the retired or nearing retirement or the very elderly," he said.

"In the last year we have had victims who are that vulnerable they have had guys who have gone out to their houses with their strong-arm tactics, so it is not all just cold calling, take the money and walk away. It is far more sinister than that and it is organised crime, so (we are) knocking it out at the earliest opportunity."

A police spokesman said that in total the force and the Met visited 25 serviced offices and checked the details of 150 firms.

They found four "virtual squatters" - firms that claim they have offices in a prestigious building but have no real link to it - one firm found to be "phoenixing" by renaming itself and carrying on trading and two companies that "mysteriously disappeared leaving all their things behind as they were in such a rush".

Sixteen thousand leaflets were also handed out to commuters outside major transport hubs during the morning rush hour, asking them to also be on the lookout in their offices.

Officers had also warned businesses in the area to look out for signs of the fraudsters, which include tenant companies that make up-front cash payments, choose short-term leases but do not put their names in reception, and operate irregular hours.

Anyone with information should contact Action Fraud on 0300 123 2040 or go to actionfraud.police.uk.