AN MP is demanding answers after claiming to have seen an official report on damage to the Furness Line - 53 hours before a train derailed while travelling at 56mph.

A Northern-operated train service was travelling between Preston and Barrow when it came off the tracks at around 6.15am on March 22.

The Rail Accident Investigation Branch is now looking into how it happened. 

So far, the investigators said the incident occurred after a section of unsupported track 'gave way' due to a cavity opening in the embankment on which the railways sits as the train passed through. A passenger on the train described this as a 'sinkhole.' 

Disruption is now expected until April 21, according to Northern. 

Tim Farron, the MP for Westmorland and Lonsdale, said he was 'deeply alarmed' after claiming to have read 'incident item 109 in report 6J89.'

It is understood Mr Farron was shown the report by a whistleblower. 

A ballast tamper, used to make tracks more level and durable, reported it had struck a water pipe at 1.15am on Wednesday March 20 - 53 hours before the incident, Mr Farron claims. 

READ MORE: Watchdog launch investigation into why Northern train derailed

In a letter to Network Rail, he said: "Given that the sinkhole appears to have occurred over a culvert which runs off Grange golf club, a source of regular flooding to the local area, there is a strong and clear link between the two here.

"Was there any intervention by Network Rail or any of its contractors to address the leak caused by this incident in the intervening period between the strike and the derailment?

"It was a relief to hear that none of the passengers or staff on the train were hurt, but I am hugely concerned that things could have been much worse - and lives potentially could have even been lost - if the train hadn't stayed upright." 

A Network Rail spokesperson said: “While the Rail Accident Investigation Branch (RAIB) investigates the cause of the Northern train derailment on 22 March, Network Rail engineers are working around the clock to repair the railway and reopen services along the economically important Furness line as quickly as possible.

“In the meantime, Network Rail and Northern remain in close contact with Tim Farron MP and other important local partners to provide them with the latest updates.”

On the line closure, a the spokesperson said: “We are expecting the line to reopen by the end of the month. The work taking place over the next few days is critical in determining a more accurate timeline. Once this is established, we will be able to advise passengers of a reopening date.

“It is expected the line will be closed until at least April 21, however, due to the complex nature of the issue, it is difficult to say for sure at this stage.”