Ryan Dilley BBC News Online

When British ships carrying nuclear fuel to Japan first stirred controversy, it was feared they might sink, or at the very worst meet pirates. Then al-Qaeda came along... When the Pacific Pintail and Pacific Teal set sail for Japan in 1999 with a cargo of mixed oxide (Mox) fuel rods, the BNFL ships were expected to be intercepted by no one more threatening than the eco-warriors of the Nuclear Free Seas Flotilla.

With the unused rods about to begin their return voyage to the UK (Japan rejected the cargo saying documentation had been falsified) more sinister eyes could be tracking the British ships' progress.

	The Pacific Teal and Pacific Pintail could sail the 15,000 miles back from Japan via: the Panama Canal and Caribbean Sea; the South Pacific, Tasman Sea and Africa's Cape of Good Hope; or around South America's Cape Horn

When Jane's Foreign Report published an article in 1999 questioning the security of the shipments, critics forced it to concede in a later issue that: "No 'Goldfinger'-style international master-criminal is likely to seize them and hold the world to ransom."

In the new asymmetric world order, born on 11 September, concerns about the transportation of nuclear material on commercial vessels now seem anything but hysterical - particularly to those nations on the ships' route.

Mox is made by reprocessing spent concentrated uranium fuel rods, separating them into plutonium, radioactive waste and the remaining unused uranium. Recombining the plutonium and uranium in Mox pellets creates a fuel capable of being returned to a power plant's reactor.

Easy pickings?

While the economics of such reprocessing - an industry in which Britain has invested heavily - have long been argued over, the interest a terrorist organisation such as al-Qaeda might show in Mox shipments has leapt to the top of the agenda.

BNFL's purpose-built ships are the most heavily armed merchant craft to set sail since World War II.

Pacific Pintail and Pacific Teal each boast three 30mm cannons capable of tackling attacking boats and aircraft. Armed officers from the UK Atomic Energy Constabulary are also on guard against boarders.

Should a frigate accompany the Mox?

Should the guards on both freighters be over-powered, would-be thieves would have to crack open the loaded vessels' reinforced hatch covers to get to the 14-inch thick steel and lead fuel flasks which are bolted to the ship's hold.

Any attempt to unload the rods would have to be made without the aid of deck cranes, which are removed before the cargo departs port.

Though such an audacious assault - even in the wake of 11 September - may seem improbable, Jane's Foreign Report concluded that even with their 30mm guns the freighters were "capable of repelling only a lightly armed attack".

Escort duty

A 1992 nuclear shipment from Europe to Japan was escorted by a large and heavily-armed Japanese patrol craft carrying two helicopters. Yet it still prompted critics to call for the job to be given to an even more formidable naval frigate.

Al-Qaeda is already thought to have been behind one daring suicide attack on a naval target, blowing a hole in the USS Cole in Yemen and killing 17 sailors. And the Moroccans say they have foiled a similar al-Qaeda plot against shipping in the Straits of Gibraltar.

Is the USS Cole attack a warning?

In light of the heightened concerns, BNFL has told BBC News Online that it has "reviewed security arrangements and made the appropriate changes".

But what could terrorists gain by attempting to hijack the Mox shipment?

A paper by the Oxford Research Group suggests a "second-year undergraduate" could extract enough plutonium from Mox to make a crude nuclear bomb.

Edwin Lyman, of the Nuclear Control Institute in Washington DC, agrees that a captured Mox shipment could be used to create a devastating atomic device.

Dirty bomb fear

"It could also serve as a radiological dispersal device, a so-called 'dirty bomb'," he told BBC News Online.

In May, the US authorities arrested an American citizen, Abdullah al-Mujahir, whom they suspected of plotting to detonate a dirty bomb - an explosive intended to scatter radioactive material packed around it.

The flasks may not deter terrorists

Mr Lyman says terrorists would not even need to remove the Mox from the rugged flasks to create a dirty bomb.

"There are munitions - shaped explosive charges - capable of breaching the casks," he says. Such an explosion would then disperse radioactive material from the ruptured container.

Mr Lyman says even a fire started around the flasks could cause the fuel pellets inside to oxidise and form an easily dispersed radioactive powder.

So how likely is an al-Qaeda attack aimed at nuclear material? "Shipment is the weakest link," says Mr Lyman, "I definitely think it is irresponsible to move Mox right now, given the situation."