The names all appeared on lists recovered from companies which the FSA believes were fraudulently selling investments.

This is the largest number of consumers the FSA has ever targeted in one go.

All names on the list were being targeted for fake or worthless shares or plots of land with the promise of great investment returns.

Jonathan Phelan, FSA head of unauthorised business, said: “These lists are nothing more than fraudsters’ phone books and people that use them are ruthless, calculated and will stop at nothing to steal your money. A call out of the blue is one of the hallmarks of investment scams, so if you ever get an unexpected call with promises of fantastic returns- you should be extremely skeptical.”

The first 10,000 letters are being sent out this week and the first 5,000 emails will be sent on 30 April. Some 19,000 of the names only had email addresses.

The letter provides tips for consumers on how to spot a scam, how to avoid becoming a victim and what to do if they have already invested money.

It also includes a leaflet on the main types of investment scams.

Any consumers who believe they have invested money into one of the schemes are advised to contact the FSA, quoting Operation Bexley.

Ten high street banks including Lloyds TSB and Royal Bank of Scotland have provided their phone number for consumers to contact.