The Financial Services Authority (FSA) has warned that more than 76,000 people could be targeted by con-men fraudulently selling them worthless investments.
The details of those who are thought to be at risk have be recovered companies that the FSA believes have been involved in selling fraudulent land and share investments.
The FSA has said that they will be contacting those who they suspect may be at risk across the following weeks via email or post.
Jonathan Phelan, the FSA's head of unauthorised business, said:
"If you get a letter or email from the FSA over the next five or six weeks, please read it - it could you save you tens of thousands of pounds. If you have already been contacted by a firm offering you a 'once in lifetime' investment opportunity or have already invested, then tell us. The information you have could help us catch criminals and shut down their scams.
"These lists are nothing more than fraudsters' phone books and the 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 sceptical.
The FSA recently released statistics showing a 19% increase year on year from 2010 to 2011 in enquiries over share scams, also known as "boiler room" scams. Urging consumers to remain wary over opportunities offered Phelan said at the time:
"We will continue to fight all forms of unauthorised business but the strongest weapon against scams remains common sense and a little bit of homework: check who you are dealing with and never forget that if it sounds too good to be true - it probably is."
Unauthorised firms are not covered by the Financial Services Compensation Scheme so if such firms go bust or simply dissappear investors could lose all of their money with no chance of recompense.