Media playback is unsupported on your device Media caption The worldwide operation was led by City of London police, Robert Hall reports

Criminal gangs who trick people into investing in worthless shares have been targeted by police in the biggest ever international crackdown on the fraud.

The operation resulted in 110 arrests - mostly in Spain and the UK.

Police targeted the masterminds and facilitators of the "boiler room" fraud - so-called because of the cramped conditions they work from.

There are 850 confirmed victims of the gangs in the UK, but the real figure is likely to be in the "multi-thousands".

Detectives say the aim of the two-year investigation, codenamed Operation Rico, is to "decimate" boiler room fraud in Europe.

They believe it is the biggest ever operation against the crime.

Image caption An Aston Martin is towed away from an alleged fraudster's home in Barcelona

Image caption A Ford Mustang confiscated by police from a property in Marbella

Operation Rico, which culminated in a series of raids this week, was led by City of London Police.

Commander Steve Head, who is the national economic crime co-ordinator, said: "It is our most important investigation ever, targeting people we believe are at the top of an organised crime network that has been facilitating boiler rooms across Europe and which is suspected of being responsible for millions of pounds of investment fraud."

Among those under investigation were 10 "tier one criminals" with alleged links to organised crime and drugs, detectives said. Nine of them are British; one is South African.

This is us seeking to decimate a crime type Detective Inspector James Clancey, City of London Police

The operation - supported by Spanish police - involved the UK's National Crime Agency and the US Secret Service.

"This is a landmark both from an investigative perspective and in terms of our close working partnership with other law enforcement agencies, most notably the Policía Nacional," said Commander Head.

Eighty-four arrests were made in Spain - where most of the boiler rooms are believed to be based - in raids involving 300 police officers, 40 of them from the UK.

Twenty people were detained in Britain, two in the US, four in Serbia.

Police released photographs of a Ferrari and a Ford Mustang seized in Marbella, and an Aston Martin recovered in Barcelona.

Detective Inspector James Clancey, from City of London Police, who was based in Spain for the operation, said: "This is us seeking to decimate a crime type."

Police say victims of the boiler room gangs have lost sums ranging from £2,000 to £500,000.

Image caption The plush Marbella home of one of the suspects targeted by police

Those who are targeted are usually vulnerable or have a history of share investment, particularly in privatised utilities in the 1980s and 90s.

Most of them are aged 40 and over, with many in their 70s and 80s. Police say some killed themselves because of the financial problems they got into.

Fraudsters cold-call their victims, applying "high-pressure sales techniques" and "confidence tricks" to persuade them to part with their money.

They are offered returns of 10 to 20% per year, directed to authentic-looking websites and glossy brochures and asked to invest in bonds in well-known firms or in other companies that are officially registered.

Initially, they may receive "dividends" to give them confidence their investment is paying off but never receive any more or get their money back.

One of the victims, a woman in her late 70s, invested £23,000 in carbon credits.

Image caption A suspect's own photo of what are believed to be high value watches worn on the end of their slippers

She was then persuaded by another salesman to borrow money to buy £140,000 of shares in gold. She never recovered the money.

"I foolishly trusted him," she told BBC News, adding: "My generation is not very streetwise - because we never had to be."

Another victim, a 72-year-old man from the Midlands, said he and his wife had been "scammed out of our entire life savings".

He said that, in the weeks after realising what had happened, "we hardly slept or ate".

"It is still very raw to us both and we both have bad days when it is all we can think about," he added.

The Financial Conduct Authority has estimated that as much as £200m is lost to boiler room frauds in Britain every year.

The biggest individual loss recorded by police was £6 million.

Officers say the fraudsters spend their proceeds on Rolex watches, Armani suits, fast cars and flashy apartments.

Some are involved in drug dealing and attend drugs parties.

Avoiding detection

Each boiler room network is believed to have an accountant, money launderer and lawyer, as well as people who do the "sales".

These tend to be university students or travellers who speak English, including some from Scandinavia, who have answered adverts for salespeople.

Image caption Police search the luxury home of a suspected criminal in Marbella

They use false names and build up a "legend" - a cover story and false history.

"They're young people who want to earn good commission and want to drink themselves into the ground," said DI Clancey.

Operation Rico is the first time there has been a multi-agency and cross-border investigation against different networks of boiler room fraudsters. Previously there was more of a piecemeal approach.

However, despite some successes, criminals had become adept at avoiding detection by frequently moving offices and wiping computers.

DI Clancey said the Spanish authorities were fully behind the operation. "The Spanish want to drive it out of Spain - it's tainting them," he said.

Detectives acknowledge that boiler room fraudsters will not disappear but they are more likely to operate in future in the more "hostile" environments of Thailand, Indonesia and the United Arab Emirates.

Police have urged anyone who may have been scammed to call the Action Fraud line on 0300 123 2040.

Anyone with any information about these crimes can call Crimestoppers anonymously on 0800 555 111.