The journalist, from the Mirror newspaper, was able to wander freely into a north-west London depot and approach unattended wagons carrying radioactive flasks of spent uranium fuel rods.

A terrorist with a real bomb could have blown up the waste, unleashing a giant toxic cloud which would have killed hundreds, the newspaper said.

Reporter Tom Parry said that the train goes largely unnoticed as it makes its weekly journey from Kent in south-east England hundreds of miles north to Cumbria.

As it sat in sidings at the London depot, he was able to place a device that could have been a bomb on the deadly 12-ton cargo, he reported. He approached the train in daylight after it was left apparently unattended for nearly 10 minutes.

The depot is just a short walk from a sports stadium, a large hospital, one of the capital's major roads and a number of housing estates, the newspaper says.

Parry said his only identification as a legitimate rail worker was a fluorescent orange jacket and hard hat, available for purchase at any hardware store. "And this was not a one-off. It was the tenth time I had wandered freely into the depot."

A spokeswoman for Direct Rail Services initially denied the reporter would have been able to approach the train. However after being presented with photographs she said: "The entire journey is protected by very stringent security. However, having seen these pictures we will speak with our security people. A full investigation will be carried out."

The affair will damage the government's bid to build a new generation of nuclear power stations, which ministers say is necessary to plug Britain's looming energy gap.

All but three of the country's existing nuclear power plants are due to come offline by 2023, leaving an energy shortfall of around 20 percent of current consumption. The government says nuclear new build will play a key role in meeting future energy needs, while also helping Britain meet its target of cutting carbon emissions, blamed for global warming, by 60 percent by 2050. Security of supply is also cited as a key advantage of nuclear power, as concerns mount over Britain's increasing dependence on imported oil and gas.

But opponents of atomic energy note that no safe way to dispose of nuclear waste has yet been devised, and argue that plants, waste facilities and carriers would be prime targets for terrorists.

The lack of security surrounding radioactive materials was demonstrated by the publication Friday of timetables for trains carrying nuclear waste.

The environmental group Greenpeace said they posted the timetables on their U.K. website to highlight the 'frightening ease' with which a terrorist could target the trains.

'Every week, trains carrying nuclear waste trundle along the U.K.`s outdated rail network through our villages, towns and cities -- often at peak times and only meters away from ordinary passenger trains,' Greenpeace said.

'(Prime Minister Tony) Blair has given the green light to a new generation of nuclear power stations, which means more nuclear waste, more nuclear transports -- and more terrorist targets.'

The transport of nuclear material was recognized by United Nations nuclear watchdog the International Atomic Energy Agency to be the nuclear operation most vulnerable to terrorist attack or sabotage, the group noted. Tests had shown the flasks of spent uranium fuel rods to be highly vulnerable to attack from armor piercing rounds.

The trains were unescorted other than by a driver and a guardsman, while the timetables could be easily worked out by anyone. They traveled on the same lines and at the same times as regular passenger or freight trains and stopped in normal stations. Members of the public or someone planting a bomb, fake or otherwise, could access them without difficulty, the group claimed.

'By taking the U.K. into a new nuclear age, Blair is putting us all at risk,' Greenpeace added.

Responding to the publication of the timetables, Liberal Democrat Shadow Environment Secretary Chris Huhne said: 'This is a shocking revelation is a dream come true for terrorists.'

He called on the government to undertake an urgent assessment of security measures, but added: 'The Liberal Democrats reject the need for new generation of nuclear power stations, which would create more waste. In a non-nuclear future, there will be no dangerous waste to transport in the first place.'

According to a report published in March, a terrorist attack on a train carrying waste nuclear materials across Britain could spread lethal radioactivity across an area of 100 sq km, and result in the deaths of up to 8,000 people.

The study, by nuclear consultants Large and Associates, noted that one terrorist cell whose plot was foiled by the security services had acquired plans of the nuclear power station Sizewell B and the locations of waste storage facilities across Britain.

'These terrorists had no reservations about the use of radioactivity to cause the mayhem and health consequences that would surely follow a successful attack on a strong source of radioactivity such as a spent fuel flask,' it said. 'If such an incident occurred in a densely populated environment, say in London, the radiation dose received by many individuals could be very significant indeed.'

In an age of international terrorism, the transportation of spent nuclear fuel could not be adequately defended against this threat, it concluded.

Related Links
Learn about nuclear weapons doctrine and defense at SpaceWar.com