British businessmen could find themselves in American jails after a crackdown by the US Department of Justice on trade with “rogue states”, leading lawyers say.

US officials are reaching across borders in an attempt to prevent companies doing business in countries such as Iran, even if people are obeying their own domestic laws.

Ali Manzarpour, a Brighton-based businessman, is in jail in Poland awaiting extradition to the United States, despite never having visited the country. He is charged with trying to export an experimental single-engine aircraft to Iran. This is not believed to have contravened any British or European law, but because the aircraft originated in the US, the Americans are claiming jurisdiction.

America’s pursuit of businesses that trade with its enemies is among post9/11 initiatives to stop the sale of materials that allegedly could be used by terrorists or rogue nations. It is also being used to prevent China gaining access to military equipment. Last month ITT, the world’s leading manufacturer of night-vision goggles, was fined $100 million (£51 million) for sending classified material to China.

American companies doing business in Iran face exceptional scrutiny after the imposition of United Nations sanctions and the country’s continuing pursuit of nuclear technology. However, companies outside the US also risk punishment for doing business with states and groups deemed unsuitable. Mr Manzarpour, who, in a separate case in the 1990s, was convicted of breaking British export rules, has been held in a Polish jail for two years while extradition hearings continue. Polish police arrested him at the request of American officials.

In a debate on the extradition in the House of Lords last year, Lord Goodhart said: “Is this not an example of the US Government’s aggressive use of the powers to obtain extradition and of the submission by too many countries — including, in other cases, our own — to those excessive demands?”

Michael Marinelli, an international trade lawyer with Cooley Godward Kronish in Washington, said that companies must be acutely aware of the identity and location of their buyers and sellers.

“The US is asserting its juristiction over people in other countries,” he said. “If you resell goods that originate in the US, then no matter what UK law says, the US says: ‘We can come after you.’

“There is a lot less tolerance for businesses saying they did not realise the sensitive nature of what they were selling.”

Cases being brought by the US Department of Commerce against companies breaching export rules indicate that, apart from rare cases, such as that of ITT, nearly all involve small operations. Companies such as Shell, which is planning a £5 billion liquid natural gas venture in Iran, and Halliburton, which had an office in Tehran for years, appear to be of less concern to authorities in Washington than an individual allegedly attempting to to sell a light aircraft.

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