More than 6,500 people across Britain have been warned by police that they could be the next victims of share fraudsters.

Detectives from City of London Police acted after uncovering a “sucker list” of potential targets for boiler room conmen.

They believe the document was being circulated among ruthless swindlers who cold-call investors and bamboozle them into buying worthless shares.

Many of the so-called boiler rooms are based overseas, making it difficult for police and the financial authorities to shut them down.

Detective Chief Superintendent Steve Head, of City of London Police, said investigators need more information about those behind the scams.

He said: “We are all potential victims for fraudsters and need to be aware of the heartless way they operate.

“Intelligence suggests that this list of people from across the UK is currently being shared among boiler rooms.”

Police said the document contained the identities of about 10,000 people, some of whom may have been culled from publicly-available shareholder lists.

Boiler room fraudsters use high pressure sales tactics to con investors with non-tradable, overpriced or even non-existent shares.

The salesmen work for unauthorised, overseas-based companies with bogus British addresses. They often use phone numbers that are routed abroad.

Anyone who buys shares through the companies risks losing their money as the unauthorised firms are not regulated and no compensation is available.

The letter was drawn up by City of London Police and the Financial Services Authority (FSA) regulator.

Jonathan Phelan, of the FSA, said customers should always check companies are registered with the watchdog.

He said: “Legitimate companies should not normally call you out of the blue offering to buy or sell shares.

“If you get such calls, just hang up and report it. These fraudsters will sound authentic, have legitimate looking websites but they just want to steal your money with little hope of you getting it back.”

:: Anyone who fears they have been contacted by a boiler room fraudster should call 0845 602 2185.