ED & F Man, the big sugar trader, said the embargo was already causing problems, obliging it "to consider what can be done with our involvement in Cuba".
BAT, which a year ago opened the first joint venture with a state-owned cigarette manufacturer in Cuba, said it was exercising all potential for lobbying and monitoring the underlying political circumstances.
Through Foreign Office pressure, as well as lobbyists and lawyers in Washington, Britain is throwing its weight into a full-scale international revolt, involving mainly Canada, Mexico and the European Union, against a new law aimed at squeezing Cuban leader Fidel Castro from power.
The so-called Cuban Liberty and Democratic Solidarity Act, also known as the Helms-Burton bill, is complex and ambiguous and there is widespread uncertainty about exactly what it will mean for those doing business in Cuba or considering investment.
But alarm at implications that appear to be potentially devastating, and anger at what is seen to have been a flouting of principles, pushed Washington's big trading allies to align themselves with Cuba and attack the law as a violation of world trade rules at the latest Geneva session of the Council on Trade in Goods of the World Trade Organisation.
Mr Clinton himself had vehemently opposed the law, sponsored by strongly anti-Castro Republican congressmen Jesse Helms and Dan Burton, until Cuban Mig fighter planes shot down two civilian light aircraft flown by Cuban Americans over the Florida Straits last month. Undoubtedly with one eye, or both, on the key Florida vote in November's presidential election, he changed tack, signed the bill and said he hoped a squeeze on foreign investments would finally bring Mr Castro down.
That brought him the hoped-for acclaim from Florida's hundreds of thousands of influential Cuban exiles but, in reality, numerous ambiguities, loopholes and provisos added by White House aides mean the new law may have little real effect.
Essentially, the law discourages foreign investors in Cuba by facing them with the possibility of law suits from Cuban exiles. Cuban Americans can sue in US courts for compensation for property or land confiscated after Mr Castro's 1959 revolution and later bought by foreign companies.
Miami lawyers estimate claims could reach a total of about $100bn (pounds 65.5bn).
It would also bar executives or controlling shareholders of foreign companies involved in any such confiscated Cuban property from entering the US.
That is the theoretical bad news for the 225 companies from 50 countries involved in joint ventures with Mr Castro's communist regime, among them 15 or so British firms, as well as potential investors such as Tate and Lyle.
Theoretical, because the good news may not only outweigh but erase the bad. For one thing, the law refers to "after the enactment of this act," apparently exempting existing investors. Secondly, Cuban Americans will be able to sue only foreign companies that have subsidiaries or holdings in the US. That rules out many, if not most of them. Thirdly, in reality few foreign companies are thought to own Cuban property. In most joint ventures, the foreign companies use factories, land or property owned by the Cuban state, such as all 175 sugar mills. (Although Cuban exiles may dispute that ownership, it would not legally affect the foreign investor.)
As if all that were not enough to calm the nerves of potential investors, Mr Clinton insisted on a clause saying the President can veto all law suits for periods of six months at a time if he considers such a move "in the national interest".
That gives Mr Clinton plenty of leeway if he wins in November. If the Republican contender is victorious, the veto is more likely to be ignored.
In terms of loopholes, the law is a veritable Emmentaler cheese and is already being dubbed by hand-wringing Miami lawyers as the Full Employment for Lawyers act.
On Capital Hill, it has also been dubbed the Bacardi act and that brings us to yet another proviso which will be welcomed by foreign investors and reveals much as to the law's true aims and origins.
Only those Cubans whose land, property or business was worth more than $50,000 dollars when confiscated (mostly in the years following 1959) have the right to sue.
That was a lot of pesos at the time and rules out the vast majority of Cuban exiles, mostly farmers or small businessmen.
It also weighs the bill heavily in favour of giant enterprises such as the Bacardi rum company, now Bermuda-based with a subsidiary in the US, and families such as the Fanjuls, who once had vast sugar holdings in Cuba.
The Bacardi family estimates its distillery, breweries and real estate in Cuba were worth $76m when confiscated by Mr Castro in 1960. Wealthy enough to have already had US citizenship by then, they will no doubt be sueing pronto.
As it happens, Bacardi co-hosted a Miami fund-raiser for the bill's co- sponsor, Senator Helms, last year and a Bacardi lawyer at first claimed to have helped draft the legislation before later opting for a more discreet silence.
And speaking of Bacardi, with so many leaks, the "Liberty act" may be on the rocks before Mr Castro.Reuse content