Rikki Nicholls, 57, and Mark Kelly, 51, devised a complex plan to persuade hundreds of workers to transfer their savings and then used the money for their own financial gain.
Victims lost anything between £10,000 and £200,000.
A court heard that some had stolen their entire pension pot, while others had to continue working to fund their retirement.
Nicholls voluntarily returned from his residence in Dubai and Kelly was arrested in May 2014 for fraud.
Scotland Yard detectives have tracked down more than 250 victims from across the UK and seized 10,000 documents following a tip from the Financial Services Authority, now the Financial Conduct Authority.
Nicholls and Kelly set up a scheme in 2007 called PCD Wealth & Pension Management with the aim of shifting clients’ pensions into mutual funds for growth.
Nicholls, a former Equitable Life employee, got details from existing customers who then called them coldly and convinced them to deposit money into a self-invested personal pension managed by their plan.
In fact, the couple sent their victims’ retirement money to mutual funds that were lucrative for them, through high commission payments.
Nicholls, of Linthurst Newtown, Blackwell, Bromsgrove and Kelly, of Maplewood Road, Wilmslow, Cheshire were convicted of conspiracy to commit fraud and transfer criminal property after a five-month trial at Southwark Crown Court.
They were sentenced to a total of six years in prison.
One victim Denis Mountford, from Birmingham, said: “When I first discovered that my pension fund was rapidly declining and inaccessible, I was very angry with myself for trusting poor financial advisers who had taken a high percentage of commission and I was also disgusted by them .
“I don’t know how you can tell if a financial advisor is completely trustworthy except through recommendations from people you can trust and I hope this case will serve as a warning to others.
“During this time, legal and investigating officers have been very helpful and considerate and have given me confidence in legal proceedings.”
Chief Inspector John Roch, head of the Met’s Economics crime team, said: “Both men put their own financial gain before the interests of more than 250 victims, losing their money and leaving some in financial ruin while earning lucrative amounts of their own.
“I would ask anyone approached by a cold caller about an investment to be vigilant.
“Consider getting independent professional advice before making a major financial decision.”
He added: “Many of the victims are vulnerable due to age and financial position, and as a result of the actions of these men, they have found themselves in serious financial difficulties. Many have to continue working to fund their retirement, or retire with a lower pension or even without retirement. These men have caused them so much suffering and fear.
“I would like to applaud the victims for their assistance in this investigation and thank those who have testified in court.
“The detectives who have worked on this case have different areas of expertise and it is thanks to their years of hard work and dedication that we have achieved this. I would like to pay tribute to the tenacity, expertise and professionalism of my employees that led to these beliefs.”
A confiscation investigation is underway, police said.
Jane Mitchell, of the CPS, said: “The damage caused by these fraudsters is enormous, with raids on the victims’ pension pots ruining their future livelihoods and their plans after retirement.
“Many victims had no pension and will have to work well past their retirement date to provide for themselves and their families.”
If you suspect you have been the victim of fraud or if you think someone is trying to access your pension, call Action Fraud – 0300 123 2040.