Local media brought the initial shipment to light in March, when a parcel of plutonium dioxide was to set sail from Cumbria, on Britain’s West coast, to Normandy, in France, aboard what was described as an ordinary auto-ferry. The Plutonium was bound for France’s Cap La Hague nuclear facility.

John Large, an independent British nuclear expert, called it "the most dangerous and worst possible material you could ship."

The Department for Transport (DFT) said last week that it had taken "regulatory action" to prohibit the shipments from Sellafield to Normandy on an unarmed ferry with few safety or security features, the Independent of London reported.

British Energy Minister Malcolm Wicks was forced to admit that the plant, designed to produce 120 tons of the fuel a year, had worked so badly that it had managed only 5.3 in five years of operation – which meant Sellafield had to turn to its chief rival, in France, to complete its orders.

The prohibition, the first of its kind, was imposed after complaints by the French nuclear safety authorities.

British Members of Parliament (MPs) condemned the initial planned shipment in May, and it was delayed for two months until it secretly took place in May, the Independent reported.

The watershed blocking further shipments occurred last Friday in Britain’s House of Commons, the lower house of parliament, before the legislative body broke for summer recess.

During debates, the news of government involvement slipped out when junior Transport minister Jim Fitzpatrick, told the Liberal Democrat MP, Norman Baker: "As a result of discussion between this department and L’Autorité de Sûreté Nucléaire regarding the shipment of plutonium by Sellafield Ltd in May, and our subsequent investigations, we took regulatory action to prevent further shipments of plutonium from Sellafield in the same manner."

British media have quoted nuclear experts as calling the shipments of hundreds of kilograms of plutonium dioxide “madness” and “totally irresponsible,” and weapons experts agree that the unarmed shipments would be a sitting duck for terrorists seeking weapons useable plutonium,

Only 10 kilograms of plutonium would be required to build a terrorist nuclear device, experts in Britain and the United States said.

Sellafield Ltd has said it is appealing against the DFT decision, saying: "We take this matter very seriously," and adding, "We are unable to comment any further."

The plans to ship the plutonium on an old converted ferry with few safety and security precautions emerged as a result of an industrial backlog at Sellafield’s reprocessing facilities.

Part of the reprocessing equation at Sellafield is the Thorp facility, which suffered a disabling leak of plutonium, uranium and nitric acid into its clarification cell in 2005. Thorp is the primary unit for separating uranium and plutonium from spent nuclear fuel, that is then sent on to be reconstituted as new fuel.

The leak of 20 metric tons of radioactive liquor into the plant’s clarification cell lasted for nine months before it was detected.

Full operations did not resume at Thorp until March 2008, but under conditions that both environmentalists and Sellafield Ltd acknowledged were substandard.

Dogged primarily by complaints from foreign reprocessing customers, like Japan and Germany, it was agreed the plant would open even though one crucial element of its operation was not ready to go – the evaporator.

Britain’s Nuclear Decommissioning Authority (NDA) and Nuclear Installations Inspectorate (NII), nonetheless, green lighted the reopening of Thorp, electing to let nuclear fuel be reprocessed to the point where it would have to be run through the evaporator.

The reconstituted fuel was simply put into buffer storage until the evaporator could be repaired and the plutonium and uranium sent further for reconstitutions as fuel.

While this solution seemed to assure Thorp’s foreign customers that they would be receiving what they paid before the plant’s closure, the NDA itself still ironically stood to lose money.

Some £560 million – or a quarter – of the NDA’s budget for closing down Britain’s aged nuclear facilities comes from Thorp’s revenues.