Among the 725 clients of specialist claims firm Rebus are those who invested in the "PPI Mis-Selling Claims 180 Day Scheme".
That promised returns of up to 12% from the pursuit of PPI claims against banks.
The scheme claimed it could take advantage of a legal loophole that meant credit agreements taken out before April 2007 were "unenforceable in law" due to a technicality.
The fund loaned investors' cash to claims management companies, which were then supposed to fast-track the PPI claims process and repay the funds within six months when claims, of a minimum £5000, were settled with the lender.
The fund was one of four run by Guardian Administration, which were placed in administration by Isle of Man regulators last July.
Rebus has estimated its clients stand to lose at least £430,000.
Martin Taylor, director at Rebus, said promotional material had claimed the fund was low-risk, and offered double-digit returns. He said: "These schemes are unregulated for a reason. They are high risk and illiquid."
Yet hundreds of Rebus clients had been advised to use their self-invested personal pensions (Sipps) to invest in unregulated collective investment schemes (Ucis) like this.
Mr Taylor warned recent legislation changes could exacerbate the problem.
He said: "With new pension rules coming in, vultures will circle and offer high returns on Ucis - people who have big pensions may not be sophisticated and may be particularly vulnerable."
David Trenner, adviser at Intelligent Pensions in Glasgow, said: "There will be people who will be persuaded to take money out of a pension into something that is taxable and inappropriate."
From January 1 promotion of Ucis, such as carbon credits, traded life policies, overseas property and fine wine, has been limited to "sophisticated or wealthy" investors.
They are defined as those with an income above £100,000, or with more than £250,000 to invest.
But Ucis funds can still be sold legally in the UK and are not subject to the same investment and borrowing rules as regulated investments, so they can invest in anything.
There is also the fact that schemes registered offshore are not covered by the Financial Services Compensation Scheme.
Despite previous restrictions and regulatory warnings, the Financial Conduct Authority estimates 85,000 people already have Ucis investments worth a collective £2.3 billion.
From next April, people with a £250,000 pension fund — worth an annuity income of around £8,000 a year — may become more attractive to those selling Ucis.
Mr Taylor said the freeing up of pension pots would "test the feasibility of the new rules surrounding the promotion of Ucis".
He went on: "We've got a particular number of clients who were advised by the same IFA and more or less 100% of their Sipps are in Ucis. Now they are worth next to nothing."
But according to Mr Taylor a continuing problem is the ease with which suspect advisory firms can become insolvent and avoid their liabilities.
He said: "When that happens, if its goes to FOS (Financial Ombudsman Service), the client can get back up to £150,000.
"However, that is only if the company that provided the original advice is trading and solvent."
Once an advisory company puts itself into insolvency and the investor is thrown back on the Financial Services Compensation Scheme, the limit is £50,000, leaving many investors nursing huge losses, Mr Taylor noted.
The only alternative is to take expensive legal action against the firm's professional indemnity insurer.
Rebus is campaigning for a change in the law to allow the personal indemnity insurance of insolvent firms to continue in operation for two years after they fail.
Mr Taylor said: "There are now strict rules on Ucis promotion. The difficulty is that the horse has already bolted — a ticking timebomb awaits thousands of people who were mis-sold Ucis in the early 2000s."
David Thomson, chief investment officer at VWM Wealth in Glasgow, said: "I had a client recently wanting to invest in a plantation in South America.
"They wanted to put money into their Sipp and use it for this. We directed them to the FCA website."
He added: "I suspect there is some good stuff but the problem is there are some cowboys out there because it is unregulated."
Even where advice was permitted in the past and an investment was suitable, it would have been allowed no more than 5% of a client's portfolio, Mr Thomson said.
The FCA said last year : "Consumers have lost substantial amounts of money investing in Ucis and similar products in recent years, so the need to introduce new rules to prevent this from continuing was essential."
This week the FCA banned two financial advisers in Wales who advised customers to invest their Sipps in unregulated and often high-risk products, regardless of suitability.
Between October 2010 and November 2012, Andrew Rees and Timothy Hughes' firm 1Stop advised nearly 2,000 customers on switching their existing Sipps worth over £112m into Sipps which permitted exotic investments such as diamonds and overseas property.
Tracey McDermott, director of enforcement and financial crime at the FCA, said hard-earned money was at risk.
He said: "By enabling customers to invest in unregulated and often high risk products without assessing suitability, these men exposed customers to the risk of losing their hard-earned pension funds."