WESTERN governments have been accused of "stunning hypocrisy" after it was revealed that Iran has a 10% stake in the world's largest uranium enrichment plant in France.

All the time that Britain, France and the US have been pressing the Iranian government to cease enriching uranium, the Islamic republic has been reaping multimillion pound dividends from its shareholding in Eurodif, an international enrichment plant at Pierrelatte in southern France.

Because of its involvement, Iran has also been learning more about the latest enrichment technology. It claims that it only wants to enrich uranium to improve its performance as a fuel in nuclear power stations, but Western nations are worried that it will be used to make nuclear bombs.

Iran's stake in Eurodif has been exposed in a report written by a French nuclear expert for the Greens and the European Free Alliance in the European parliament. Documents confirming the connection have also been seen by the Sunday Herald.

They show that in 2006, Reza Aghazadeh, Iran's vice-president and the president of the Iranian Atomic Energy Organisation, was replacing the Iranian representatives on the board of Sofidif, a joint French-Iranian company with a major stake in Eurodif.

According to a meeting of Sofidif in June 2006, the purpose of the company was "to participate in the study, the realisation and the operation of uranium enrichment plants based on the French gaseous diffusion technique".

Other papers show that in 2005 Sofidif's investment in Eurodif yielded £12 million in dividends. Eurodif, formed by France, Belgium and Spain in the 1970s and run by French nuclear company Cogema, enriches uranium for 100 reactors in France and worldwide.

At the same time, Iran has been accused of breaching its obligations under the nuclear non-proliferation treaty by enriching uranium at a plant at Natanz in central Iran. Last week, the United Nations discussed moves to toughen sanctions against the country in an attempt to force it to shut the plant.

Mycle Schneider, the Paris-based nuclear consultant who wrote the report for the MEPs, was shocked by what he discovered. "The continuous deep involvement of Iran in the world's largest multinational uranium enrichment plant in France is the perfect illustration of the stunning level of hypocrisy that has governed the non-proliferation treaty," he said.

The point was reinforced by Dr David Lowry, a nuclear proliferation specialist based in Surrey. "The hypocrisy of France, as a nuclear technology supplier to Iran, ganging up on its customer client with the other self-appointed permanent bully-boy' members of the UN Security Council would be funny if it wasn't so serious," he said.

Rebecca Harms, vice-president of the Green group in the European parliament, said: "It's time to stop pretending that there is a fundamental difference between the peaceful atom and nuclear weapons. It is not only operating uranium enrichment facilities that provide the basis for a nuclear weapons programme, it is nuclear technology and know-how that paves the way to the bomb."

Schneider's report also exposes details of an extraordinary nuclear experiment run by the US in the 1960s. Two PhD students without any nuclear expertise were asked by a leading nuclear weapons laboratory in Berkeley, California, to design a nuclear bomb using publicly available sources.

"The goal of the participants should be to design an explosive with a militarily significant yield," said a declassified US report from 1964. The project was known as the "Nth Country Experiment", as it was attempting to assess the risk of new countries developing nuclear weapons.

It took the students concerned, Dave Dobson and Bob Selden, two and a half years to come up with a design. It was judged by scientists from the US nuclear weapons laboratories to be a credible and workable bomb.

It would be too big to be fired on a missile, they concluded, though it could be delivered by plane or truck. The bibliography, compiled by the students from open sources, remains classified.