Passengers using trains through Northampton and Milton Keynes are being warned to expect delays and cancellations until at least noon today (Sunday) following damage to overhead wires on the London Euston route.
London Northwestern Railway and Avanti West Coast services heading north towards Rugby, Coventry and Birmingham are also disrupted due to over-running engineering works.
A spokesman for National Rail said: " All lines have now reopened following damage to the overhead electric wires between Milton Keynes Central and Watford Junction.
"But trains between Coventry and Watford Junction may still be cancelled or severely delayed by up to 90 minutes. Major disruption is expected until at least 12 noon on Sunday."
A London Northwestern Railways spokesman added: "Road transport has been requested in both directions between Coventry, Rugby, Long Buckby and Northampton.
"We also have 12 vehicles connecting stations between Northampton and Watford Junction, again in both directions."
Passengers are being advised to check journeys on the National Rail Enquires journey planner before setting out.