Shinder Singh Gangar, 46, and Alan White, 49, were convicted at Sheffield Crown Court of conspiracy to defraud .
Both men, who worked for accountants Dobb White & Co with offices in Leicester and Nottingham, had denied the charges.
The court heard the pair had set up a classic “Ponzi fraud” where investors were duped into investing into an investment scheme that did not exist.
The scheme was kept going when money from new investors was used to make interest payments to previous investors. The bulk of the money was then invested offshore.
Fraud squad detectives who investigated the scheme say as much as £100m may have been duped from innocent investors.
Evidence was given that the pair used the money on high living, buying properties and investing in speculative schemes.
The court was told that Gangar had offered potential investors returns of up to 160 per cent. Many who invested were not wealthy and used money put aside for their retirement.
The fraud began to unravel when the pair attempted to bribe a US law enforcement officer when part of their scheme was threatened with exposure in the US.
Sentencing, Mr Justice Langstaff, said: “Gangar was the salesman who possessed great ability and personal charm.”
This fraud was deeply corrosive. The defendants obtained money from victims that many could ill afford to part with, for instance, money set aside for retirement funds.”
The Serious Fraud Office has indicated it will begin proceedings to confiscate the illegally gained assets from the pair.