Guppy faces a maximum of a further seven years inside if he continues to keep silent about the location of assets estimated to be worth up to pounds 2m.
John Alexander, a senior insolvency practitioner with accountants Pannell Kerr Forster, was appointed Guppy's trustee in bankruptcy at the end of July.
He warned yesterday: 'Guppy might not have realised when he applied for bankruptcy that if he withholds information from me about his assets I can go to court. Anyone found guilty of withholding assets from creditors in a bankruptcy can get up to seven years in prison.'
Guppy, who was best man at Earl Spencer's wedding, was convicted in February 1993 of an insurance sting three years earlier, involving a staged jewellery robbery in New York. Together with an accomplice, Benedict Marsh, Guppy claimed pounds 1.8m from Lloyd's of London to cover jewels 'stolen' by another accomplice.
In April this year Guppy applied to the court for a reduction in his sentence, but although his fines were reduced, he failed to get his sentence cut, largely because he had not returned the money defrauded from Lloyd's. He has paid back barely pounds 20,000 to date, according to Mr Alexander.
In June, Guppy applied to be made bankrupt, a move that would release him from his debts after a three-year period. Lloyd's then nominated Mr Alexander to pursue his assets.
Mr Alexander said: 'There might be pounds 1m-pounds 2m around somewhere.'