The four MPs including Green MP Caroline Lucas have written jointly to the Financial Conduct Authority demanding it take action in the case.
The pensioners have been denied compensation by the Financial Services Compensation Scheme and the FCA has previously claimed there was nothing it could do.
The MPs, Ms Lucas and Tories Derek Thomas, Simon Hoare and David Warbuton all have constituents who have lost hundreds of thousands of pounds.
The pensioners come from the MPs constituencies in Sussex, Cornwall, Dorset and Somerset.
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The letter to FCA chief executive Nikhil Rathi highlights the plight of the pensioners saying, “many now find themselves in penury through no fault of their own.
“Compensation remains long overdue for these victims who have lost their life savings.”
The letter accuses the FCA of failing to monitor or investigate the financial advisers or accountancy firms involved in the loss.
The letter adds: “One of (the FCA’s) chief objectives is to protect consumers by setting rules and standards for financial firms to follow.
“We are at a loss to understand why the FCA feels it cannot intervene. We urge that this is reviewed and that due weight be given to the circumstances we have outlined.”
Accountant Nick Moger, representing the victims, said: “It is vitally important that the FCA look at this again.
“Many people have lost their life savings at a time when they can least afford to do so.
“The way in which the relevant authorities have washed their hands of this case when it is their job to protect the consumer is frankly disgraceful.”
David Warburton MP said: “Financial fraud is a serious and devastating crime for those who fall victim to it.
“As this is an ongoing case I can’t comment further, but I sincerely hope justice will be served for those who have been affected.”
An FCA spokesperson said: “We take allegations of fraud and unauthorised individuals doing regulated business very seriously.
“We will respond to the letter in due course and continue to assist law enforcement in their work.”
Last month, a former financial adviser pleaded not guilty at Salisbury Crown Court to 28 counts of fraud against 19 former clients totalling £5,016,770 between 2011 and 2018.
He was given unconditional bail and will face a trial in April next year.
