The train derailed at Torness Power Station

Two of the wagons on the train derailed and BNFL said one of these was carrying a nuclear flask.

The company said the emergency services had been called and the area was monitored as a precautionary measure.

A spokesman said there was "absolutely no damage" to the flask.

Doug McRoberts, a spokesman for British Energy which owns and operates the Torness plant, said the train was reversing when the wagons came a few inches off the line.

He said: "We have plenty of capacity to store fuel and we don't think it will take a long time to get the wagons back on to the rail line.

"The train had been reversing into the railhead when the wagons at the back end became derailed."

Used nuclear fuel

Janine Claber, spokeswoman for Direct Rail Services, said all spent nuclear fuel is transported in heavily shielded, purpose-built containers known as flasks, each weighing more than 50 tonnes.

A spokesman for British Transport Police said the train was travelling at a low speed north from Carlisle.

It had been used to take used nuclear fuel to the Sellafield plant in Cumbria.

A spokesman for Lothian and Borders Police said the derailment posed no threat of contamination.

He said: "The area was quickly cordoned off, train services were suspended.

Officials said there was no contamination risk

"Experts from Torness nuclear power station went to the location.

"After tests they confirmed that there was no external contamination and the integrity of the flasks had not been breached."

Recent problems caused by severe weather in Scotland and northern England have also added to the misery for cross-border rail travellers.

The incident came amid continued concern over the safety of the railways.

A major programme of track inspections and re-railing was undertaken in Scotland and England after the Hatfield crash which resulted in four deaths.