Rail services on the East Coast Main Line have been severely disrupted by problems with overhead power lines.
East Coast, Grand Central and First Hull Trains are starting and terminating at Peterborough, meaning they are unable to run between Peterborough and King's Cross.
First Capital Connect are running shuttle train services between Letchworth Garden City and Cambridge, between Biggleswade and Peterborough and between Welwyn Garden City and King's Cross.
Buses are replacing trains between Letchworth Garden City and Welwyn Garden City and between Letchworth Garden City and Biggleswade.
Trains between Stevenage and Luton and between Stevenage and Hertford North are also being replaced with trains.