A gold and currency trading firm which authorities worried was a fraud has been put into liquidation.

PTT, or Prosper Through Trading, has been in the hands of receivers since August after the Financial Markets Authority went to the High Court to freeze its assets, as well as those of four associated entities and of Steven and Lisa Robertson.

It later emerged that the FMA has serious concerns that the company was running a "fraudulent scheme designed to obtain money from members of the public".

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These concerns, according to a judge, arose from a complaint to the FMA that Steven Robertson was operating a "Ponzi scheme" through PTT and other entities.

The FMA's investigation is ongoing, a spokesman confirmed today.

A report by receivers John Fisk and David Bridgman to the High Court was made public in October and said Robertson, who appears to control PTT, arranged for staff to hold directorships and shareholdings as nominees for him.

About $4.4 million had come into PTT and associated companies between June 2013 and August last year, which at this point had only $51,000 of cash, the report said.

Fisk and Bridgman, in the report, recommended that PTT and the other entities be put into liquidation, which was ordered by the High Court last month.

The liquidation, Fisk said this afternoon, would give him extra powers to investigate earlier transactions.

The Herald revealed last September that a Bentley Continental and a late-model Mercedes-Benz were among assets frozen as part of the FMA's probe into PTT.