The Pensions Regulator is advising savers to avoid small self-administered schemes (Ssas), branding them insufficiently regulated and an easy target for scammers.
Instead, TPR is urging consumers to opt for Self-invested personal pensions, which, unlike Ssas, are regulated by the Financial Conduct Authority.
The regulator's warning came as a government policy, announced in the Autumn Statetment on 23 November, sought to clamp down on the use of dormant limited companies as the sponsor employer of a Ssas.
A number of providers have also called for Ssas to be brought under the auspices of the FCA.
A spokesperson for TPR said: "Single person Ssas schemes are not regulated by the FCA which is why we strongly urge consumers who wish to control their pension scheme investments to instead use Sipps offered by FCA-authorised providers, and in all circumstances to take advice from qualified financial advisers authorised by the FCA."
The spokesperson said, under current regulations, consumers who were scammed through a Ssas would "in the vast majority of cases" lose all their money.
As workplace schemes, Ssas do technically fall under the jurisdiction of TPR. However the spokesperson said TPR's regulatory focus had "historically tended to be on larger schemes, with Ssas included mainly where we are concerned about pension scams".
Ssas with two or more members have to register with TPR. However, that does not mean TPR assesses the scheme. If the Ssas has only one member, it only needs to register with HMRC.
Murray Smith, sales and marketing director at Sipp and Ssas provider Mattioli Woods, agreed that scammers were increasingly shifting their attention to Ssas, following the FCA's clamp down on Sipps.
However, rather than restore the old pensioneer trustee regime of Ssas, as others have argued, Mr Smith said it would make more sense simply to pass regulatory responsibility to the FCA.
"The FCA should regulate Ssas providers in the same way they do Sipp providers, because actually a lot of Sipp providers are also Ssas providers," he said, adding: "There is no difference between a Ssas and a Sipp as far as we're concerned."
Christopher Foster, a partner at Pennines Independent Financial Advisers, agreed pension liberators had shifted their attention from Sipps to Ssas.
Mr Foster said: "Sipp companies are more careful about this area now and at least two of the latest I have seen involved clients opening a limited company then a Ssas in order to avoid regulation."
He said members of Ssas needed the same protections as Sipp members, and should "absolutely" be regulated by the FCA.
Jeff Steedman, head of Sipp and Ssas development at Xafinity, also said Ssas needed better regulation.
"I would suggest that Ssas is not really policed that closely by HMRC. Every year, a Ssas has to submit an annual pension scheme return [to HMRC]. What do they do with that data? On the face of it, not an awful lot," he said.