Bletchley derailed train 'going too fast' says Network Rail
A freight train engine which derailed on the West Coast mainline at Bletchley may have been going too fast, Network Rail has said.
The line has partially reopened after being closed for more than 12 hours, causing major delays.
Rail passengers are warned to expect further delays, which could run into the weekend.
The Freightliner locomotive appeared to have approached a set of points at high speed, a Network Rail spokesman said.
He said that this caused the tracks to buckle, damaged wooden sleepers and brought down some overhead cables.
"You are meant to approach points at a relatively low speed," the spokesman said. "But it looks like that move was taken at a high speed and, as a result, the train has derailed."
Two lines open
Limited rail services between London Euston and Milton Keynes have resumed.
All London Midland, Southern and Virgin rail services were cancelled after the incident at Bletchley south junction shortly before 02:30 GMT.
Two trains an hour will run from London to Manchester Piccadilly and Birmingham until further notice. One train an hour will run between London and Liverpool Lime Street
The driver was the only person on board the electric locomotive and is being treated for injuries.
The engine was not pulling any freight or carriages.
Engineers have now cleared two of the four lines damages in the incident, which has allowed some services to begin running.
The engine is upright but blocking the line until heavy lifting equipment can be brought in later to remove it from the tracks.
The Rail Accident Investigation Branch is conducting an investigation.
The Freightliner engine was being operated on behalf of Virgin trains, hauling some of its older trains.
Passengers are being advised to consult National Rail Enquiries if they intend to travel.