Man has indicated to the City that it is no longer financing Cuba's sugar crop because of fears over the US Helms-Burton Act, introduced a year ago.
Industry sources say, however, that Man has instead routed its Cuban business through a London-based firm, Pacol, run by its former top sugar trader, to disguise its involvement.
Mystery surrounds Pacol's beneficial ownership, however, and the secrecy raises a number of corporate governance issues.
Man has refused to answer any questions from the Independent on Sunday since its interim results last November.
Last month, its public relations advisers Financial Dynamics, the City's biggest PR firm, resigned in frustration at the group's reluctance to communicate.
Man came to the market in 1994, but the shares have been disappointing, largely because it remains poorly understood. The secrecy over Cuba, and the country's hitherto undisclosed importance to Man, will only reinforce UK institutions' reluctance, analysts say.
Now worth pounds 480m, Man deals in a range of commodities around the world. Sugar, however, is by far the most important, accounting for pounds 45.5m of last year's pounds 81.1m pre-tax profit. Of that, insiders say, about 55 per cent - just under a third of total profits - originated from business with Cuba.
Man also has at least $50m (pounds 31m) invested in financing the Cuban sugar crop, sources there say.
Despite Cuba's importance, Man has made no announcements over Pacol or its sister firm, Pacol SA, based in Paris.
Pacol's London operation is headed by Christopher Murphy, who resigned as Man's chief sugar trader last October.
The firm's ownership remains unknown, however, and the sole director is Napleton Holdings, a Guernsey-registered company.
Mr Murphy is also a director of Pacol SA, whose ownership is similarly unclear.
The Helms-Burton Act threatens to punish foreigners who do business with former US-owned properties that were nationalised by President Castro after Cuba's 1959 revolution.
The new law has caused a huge international row and last November, the European Commission issued its own directive seeking to make it illegal for firms to co-operate with the US.Reuse content