Three of the defendants were found guilty today for their part in the scam, and three more plead guilty earlier.
The defendants, who cannot be named because of on-going criminal trials, were found guilty of a range of crimes including conspiracy to defraud, fraud abuse by position, perverting the course of justice and money laundering.
Three of them also pleaded guilty to communicating and invitation to engage in investment activity, contrary to the financial services markets act 2000.
All six will face sentencing at Southwark Crown Court and confiscation proceedings at a later date.
Yesterday, it was revealed that the value of FCA fines has risen tenfold in the last year, with the authority handing out a total of £229.4m in 2017.