Protesters prepare for chase as plutonium ships near UK

Anti-nuclear protesters are preparing for a game of cat and mouse with French and British authorities as two ships loaded with weapons-grade plutonium approach the Channel in the next few days.

The two British ships, with an escort of Royal Marine commandos, are transporting 140kg of military-surplus plutonium - enough to make 30 nuclear warheads - for experimental conversion to nuclear fuel in the south of France.

The ships, which left Charleston, south Carolina, on 20 September, are designed to carry radioactive materials. Their progress across the Atlantic is being monitored by satellite and aircraft.

A Greenpeace ship, L'Esperanza, and a flotilla of yachts, hope to impede the plutonium shipment before it reaches Cherbourg for a 600-mile road journey to a nuclear processing plant in the Rhône estuary.

The precise whereabouts and movements of the British-flagged, nuclear transports - the Pacific Teal and the Pacific Pintail - are being kept secret to prevent protesters from intercepting them at sea. Greenpeace officials expect the ships to dock in Cherbourg this weekend, probably at night.

"The US and France are unnecessarily threatening international security and the environment. There is no conceivable justification for this transport," said Shaun Burnie of Greenpeace International.

The US will have no capacity to convert military plutonium into nuclear power station fuel - a process never attempted before - until next year. Washington has awarded a €243m (£167m) experimental contract to convert the plutonium into fuel for nuclear reactors - mixed oxide fuel or Mox - to the French company, Areva. Once converted, the fuel will be shipped back to the US early next year.

The contract for transporting the material has been awarded to a British company, whose ships are - exceptionally - being guarded by a unit of Royal Marine commandos.

Greenpeace and other anti-nuclear campaigners say that the movement of weapons-grade plutonium half the way around the world in this way is an invitation to catastrophe: either a radioactive leak or an attempt by a terrorist group to seize the shipment to make a nuclear bomb of its own.

Protests are planned all along the route from Normandy to the Rhône estuary but the plutonium is expected to travel at night along a secret route.

The consignment represents a tiny portion of the 34 tons of excess weapons grade plutonium which the US must dispose of as part of a disarmament agreement with Russia.

Jacques-Emmanuel Saulnier, a spokesman for Areva, accused Greenpeace and other "militant ecologists" of hypocrisy. He added: "They fought for years for the elimination of military-grade plutonium and now they are protesting against a process which is part of that elimination".

Greenpeace says that military-grade plutonium should not be recycled for peaceful purposes but mixed with radioactive waste, solidified or vitrified, and stored.