The Serious Fraud Office is examining a con that took in Sven-Goran Eriksson and the North Korean government, BBC Panorama has learned.
Investigators are also looking at how the same conman stole a football club and broke a bank.
Convicted fraudster Russell King persuaded the former England manager to join Notts County FC as director of football and to visit North Korea.
Mr King denies any fraud and said he was just a consultant on the deals.
Mr Eriksson was appointed at Notts County in 2009 following a takeover that promised to bring millions of pounds of Middle Eastern investment.
"For me as a football man it was fantastic, building a club from the bottom of League Two and having the funding to do it, to be a Premier League club. It's like a dream, so I signed. Big mistake," he said of the deal.
The promised money never arrived and the club was left £7m in debt. Mr Eriksson says there were early signs that all was not as it seemed.
"I started to have doubts when they came and told me the milk bill has not been paid," he said.
Mr King claimed his Swiss-based mining company had assets worth almost $2 trillion because it had the rights to North Korea's gold, coal and iron ore.
He told Mr Eriksson the Notts County cash would come from that mining deal. He then persuaded him to join a delegation visiting Pyongyang.
"I was in the palace and they were handing over to the North Korean government so-called shares," Mr Eriksson told Panorama.
"I asked them how much that was and what they told me was not millions, it was billions of dollars. They used my name. Of course they did. At the end it became a big, big mistake."
Russell King's business deals had credibility because they appeared to have the backing of First London plc, an investment bank with advisers including Conservative MP Tim Yeo and Air Marshal Sir John Walker, a former British spymaster.
The bank sent Sir John, a former head of defence intelligence, to check out Mr King and the Korean deal, but he was also taken in.
Sir John said of the deal: "What do I think of Russell King? Not a lot. He was good at chat, but that was his business. He was a con man. I was taken the same way Sven was taken. They just wanted names."
Mr King also managed to get control of almost half of First London plc without paying a penny for the shares, after he convinced its bankers he was managing billions of dollars for the Bahraini royal family.
But Fawaz Al Khalifa, President of the Bahraini Information Affairs Authority, says that Mr King was lying about his royal connections: "He might have met members of the family here or there, but we have no financial connection to him or his company."
First London PLC went into administration last year with debts of £8.7m and the Financial Services Authority (FSA) has been examining the deal that gave King control of 49% of its shares. The FSA has now passed its finding to the Serious Fraud Office (SFO).
"In this case the acquisition of control occurred without the FSA having been given the prior notice which the law requires it to be given," said an FSA spokesman.
First London plc's parent company, First London Group plc, is still in business. In a statement, its lawyers said the failure to notify the FSA about the change in ownership was a mistake that had been rectified:
"This was simply an error and not done for any ulterior or questionable motive. As far as our client is aware the FSA were satisfied that the information provided was in compliance with all legal and regulatory requirements.
"Our client is unaware of any investigation by the FSA or SFO."
Mr King, who was jailed for insurance fraud in 1991, denies any involvement in the running of Notts County or First London plc.
But Panorama has obtained dozens of emails and numerous testimonies that show he was secretly pulling the strings at Notts County.
King even referred to himself as Lord Voldemort, the character from the Harry Potter books who can never be named.
The club had been owned by a supporters' trust, but Mr King persuaded the fans to sell it for just £1 after they met one of his supposedly wealthy benefactors in Bahrain.
Abid Hyat Khan was introduced as a Middle Eastern prince, but Panorama has discovered he is actually on the run from British police.
He absconded from the UK in 2008, when he was due to stand trial for allegedly stealing almost £1m. Khan denies posing as a prince.
Panorama: The Trillion Dollar Con-Man, BBC One, Monday, 18 April at 2030BST and then available in the UK on the BBC iPlayer.