A young passenger is helped off the train after the accident

The accident happened at about 0315 GMT and affected the London to Inverness service, which left Euston at 2002 GMT.

About 240 people were on board. Passenger Russell Sharp, said: "It was a miracle it was not derailed."

The train was moved to Carstairs station at 0940 GMT. First ScotRail said buses were taking passengers to Aberdeen, Inverness and Fort William.

The incident happened at Beattock Summit, south of Carstairs.

'Incredibly lucky'

British Transport Police (BTP) are investigating the accident.

A spokesman said the object on the rails was probably a roll of material used for lining the track.

Mr Sharp, a freelance picture editor, said: "It caused major damage to the train and caused the train to come to an abrupt stop."

A picture after the accident taken by passenger Russell Sharp

"We were apparently going at 80 miles an hour at the time so it's incredibly lucky that I'm actually able to talk to you now."

A spokesman for BTP said officers were investigating the possibility the material had been blown onto the track.

They will also consider whether the material had been put there deliberately.

The spokesman added that while maintenance work had been carried out in the area recently, it was regarded as "highly unlikely" that the material had been left on the track by workers.

A Network Rail spokesman said: "The train struck some material on the line and failed.

"The incident is being investigated."

A spokeswoman for First ScotRail confirmed the train was travelling at about 80 mph when it hit an obstacle on the track.

"Food and refreshments were provided," she added.

"Passengers' details have been sourced and refunds will be made."