Commuters can expect "major congestion" this morning due to signalling problems on a busy rail route.
Some trains have been cancelled, while others may be delayed on the West Coast Mainline route between Northampton and London Euston.
Signalling problems in the Bletchley area mean there will be disruption "until further notice", London Midland said.
Passengers have been advised to travel only if it is essential, they added.
London Midland will run two trains an hour in both directions, while Virgin Trains had to cancel some services between Milton Keynes and London Euston.
While Virgin Trains have since said some signalling has been restored it added that cancellations may still occur.
Passengers with London Midland tickets will be accepted on East Midland Trains, London Overground and some London Underground routes, and are advised to check before travelling.
In a statement the company said: "London Midland is working closely with Network Rail to resolve the issue and we apologise if your journey is affected."