Investigation into the Tebay crash

The workers were hit after the wagon came loose at a yard several miles away and ran away down a hill near Tebay.

Police say the alarm was raised at the yard, but did not reach the men on the track in time.

The line is shut between Oxenholme and Penrith and trains between Glasgow and the south are delayed.

Ten men were working in the group when the accident occurred at 0605 GMT on Sunday.

It's very unlikely they would have known anything about it until the trolley hit them Mark Lenderyou Heath and Safety Executive

They were under arc lamps and the trolley would have come out of the dark.

Mark Lenderyou of the Health and Safety Executive said the runaway vehicle would have been running "virtually silently" - while the men were working amid the noise of lighting generators.

"It's very unlikely they would have known anything about it until the trolley hit them," he added.

The names of the four men who died, all from Cumbria and Lancashire, are due to be released on Monday morning.

Track workers who saw the unmanned vehicle, which had no brakes, heading down the track were unable to alert staff downhill.

Inspector John Vernon of the British Transport Police (BTP) told BBC News24 that the alarm was raised when the trolley escaped from the depot, but the message did not reach the men working on the track in time.

The trolley was part of an operation of loading and unloading metal rail onto railway wagons, he said.

The trolley eventually stopped one mile further on from the collision.

The BTP has begun an investigation with Cumbria Police and the Health and Safety Executive, which will focus on why it ran away with disastrous results.

The men were employees of rail infrastructure company Carillion Rail and were not working on the £6bn modernisation of the West Coat line.

Questions

The firm said it was co-operating fully with the investigation and their primary concern was for the families of the dead and for the injured.

Late on Sunday, a team was back at the site of the accident using oxy-acetylene cutting equipment under arc lights to remove sections of rail, said BBC correspondent John Thorne - the same task that a 10-man squad was carrying out when it when it was hit by the runaway trolley in the morning.

The inquiry into the Tebay rail deaths must first ask how the trolley which struck the men became detached and was able to run away downhill, transport expert Christian Wolmar told BBC News 24.

Emergency vehicles at the scene of the fatal crash

Normal goods wagons stop when their trains break apart, he said, and the inquiry must ask if the brakes were disconnected in this case, or if that kind of brake was not being used, or if the trolley had stopped and chocks had not been put in properly.

"It's unforgivable," he added.

A second question was why the gang working in the path of the runaway vehicle had not been contacted, Mr Wolmar went on.

The BBC Travel Unit said Virgin West Coat and Cross-country services were being replaced by buses over the affected route.

Journey times to Penrith and Glasgow from the south are expected to be increased by up to 90 minutes.