TPR believes that about 370 people have been persuaded to transfer around £18m into eight pension schemes at the centre of the case.
The regulator says there is evidence that members’ funds have been passed on to companies connected to the suspects in this investigation.
TPR opened a case after a number of legitimate schemes received requests from members to transfer their savings into suspicious schemes and reported it to TPR.
On 11 December warrants were executed at two homes in Essex in a TPR-led joint operation with Essex Police.
A business address was also searched.
Four people – three men and one woman – were interviewed under caution and a further two men were arrested and questioned, all on suspicion of fraud offences.
They were released while the investigation continues.
As part of the same investigation, on 10 December TPR’s Determinations Panel suspended nine people from acting as trustees for a period of 12 months, and appointed an independent trustee to the eight schemes at the centre of the investigation.
Nicola Parish, TPR’s executive director of frontline regulation, said: “The legitimate schemes in this case did the right thing by raising their concerns with us and stopping their members transferring out and potentially losing their life savings in what we believe to be scams.
“If you are trying to transfer out of a pension scheme and your existing scheme is raising concerns you should listen to them.
“They are protecting your pension and any red flag warning signs should be taken very seriously.”
Anyone who is concerned about their savings in a pension scheme, or thinks they may have been the victim of a pension scam, should call Action Fraud on 0300 123 2040.