Two British freighters are on their way to the UK from Japan with a cargo of used nuclear fuel - and a challenge by environmentalists has been dropped.

Greenpeace called off a High Court action to prevent the consignments of weapons-usable plutonium being shipped to the UK because the vessels had already left Japan.

The British Nuclear Fuels (BNFL) ships will take six weeks to reach Sellafield, where the fuel was first processed.

In 1999, 250kg of fuel, known as MOX, caused a diplomatic incident between Japan and Britain when it emerged that BNFL workers had falsified safety data.

To send highly radioactive materials on a six-week trip on the high seas was a stupid idea before 11 September

Pete Roche Greenpeace

The Japanese rejected the shipment and insisted it had to go back to the UK before they buy more fuel from BNFL's new �470m Sellafield MOX plant.

Lawyers for Greenpeace had been preparing to apply for an injunction to stop the shipment, which the group described as a "floating target for terrorists", leaving Japan.

The campaign group said the cargo had been "sneaked out" of Japan hours before a judge was due to decide on the injunction.

But BNFL said Greenpeace had had "ample opportunity to take legal action... but chose not to".

Greenpeace is expected to seek permission to apply for a judicial review of the Environment Agency's decision not to treat the material as radioactive waste and not to follow the required procedure for nuclear waste imports.

'Furious'

The BNFL vessels, the Pacific Pintail and Pacific Teal, are equipped with naval guns and guarded by anti-terrorist police.

BNFL has told the Environment Agency it intends to recover the plutonium and uranium within the MOX.

The ships will be guarded by police

Greenpeace and local environmental groups staged protests in Japan against the shipment, which they claim could be made into 50 nuclear weapons.

They want MOX to be classed as radioactive waste, because no use has been forecast for it and Britain has huge stockpiles of uranium and plutonium.

Greenpeace nuclear campaigner Pete Roche said the ships would be a "floating target for terrorists".

He added: "To send highly radioactive materials on a six-week trip on the high seas was a stupid idea before 11 September.

"In today's context it can only be described as insane."