Travel disruption is continuing after a freight train engine derailed on the West Coast mainline in Buckinghamshire.
The line was partially reopened on Friday afternoon after being closed for more than 12 hours following the incident at 02:30 GMT in Bletchley.
Operators affected include London Midland, Southern and Virgin trains.
A spokesman for Network Rail said the Freightliner locomotive appeared to have approached a set of points at Bletchley south junction too fast.
This caused the tracks to buckle, damaged wooden sleepers and brought down some overhead cables.
There is as yet "no estimate for the completion of repairs and therefore it is not yet known whether services will continue to be affected on Sunday", according to the National Rail Enquiries website.
There is an amended service operating between Milton Keynes Central and London Euston.
Virgin is operating a reduced service between London, Birmingham and Manchester Piccadilly.
Southern trains will start and terminate at Watford Junction, so will not run between Milton Keynes Central and Watford Junction.
London Midland is also operating a revised timetable.
"You are meant to approach points at a relatively low speed," the Network Rail spokesman said.
"But it looks like that move was taken at a high speed and, as a result, the train has derailed."
The driver was the only person on board the electric locomotive, which was not pulling any freight or carriages, and is being treated for injuries.
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.