Leahy, a former accountant with Coca-Cola who now lives in Sligo, was one of hundreds of investors, including other Irish individuals, who lost substantial amounts of money after forensic accountants found no trace of up to 500m in assets that Langbar . . . which had been co-founded by former executive chairman Mariusz Rybak . . .claimed to hold in Brazil and the Netherlands.

The UK's Serious Fraud Office is now investigating the company, while a new executive chairman, David Bulcher, is trying to trace the money on behalf of investors.

Leahy is understood to have spent over 1.5m to acquire derivatives in Langbar, but has contested that the money should be returned to him as the shares to back those derivatives never existed.

Bulcher is suing Rybak, who is a Monaco resident, as well as another former director, Jean-Peirre Regli, and Langbar's primary financial backer, Abraham Arad Hochman, for over 40m, claiming "deceit and conspiracy to defraud".

Leahy told an English newspaper early this year that the market had been "raped" and described the events at Langbar as "outrageous".

Shareholders have been infuriated at Leahy's arrest in Monaco on what were widely considered to be flimsy charges. Another investor who was travelling with Leahy at the time, Ted Maye, was also arrested. He too is expected home in Ireland this week.

It is understood that the Monaco judge assigned the case has apologised to Leahy for his detention. He was held in a French prison, as Monaco's only detention centre was full. He is believed to have lost some weight, but is relieved that he will be returning home this week.

His wife is pregnant with their first child. A Langbar shareholder action group has been campaigning for the two men's release.

Worldwide personal assets and bank accounts belonging to Rybak, Regli and Hochman have already been frozen, but it is believed that many assets may already have been redistributed before being subjected to court orders.

The alleged fraud at Langbar, which stunned the UK financial world, first emerged last October. The company's accountants refused to sign off the accounts and resigned as auditor over concerns at Hochman's involvement in the firm.

Hochman owned 59% of Langbar. Early in 2005, Langbar appointed risk-consulting firm Kroll Associates to verify purported cash deposits of over 500m with Banco do Brasil and a unit of ABN Amro. Kroll said it wasn't able to find any evidence that Langbar had any entitlement to relevant assets and police were subsequently informed of a suspected fraud.

Shareholders have been angered over the involvement of Rybak's daughter in the firm, while Rybak sold millions of euro worth of Langbar shares just before the stock was suspended.

Rybak, who was born in Poland, was previously involved in a number of Canadian enterprises.