Rail commuters going south on the East Coast Mainline experienced hours of delays due to overhead wire problems.
Engineers worked throughout the night to repair the damage to the line near Peterborough and minimise delays to services into London's King's Cross.
The problem has now been fixed, and National Rail said all knock-on delays had now finished.
Those affected by the problem were East Coast, First Capital Connect, First Hull Trains and Grand Central.
Several First Capital Connect trains were cancelled while others were delayed by up to two hours.
Some East Coast services were delayed by up to four hours.
The problem developed just after 18:00 BST on Monday between Peterborough and Stevenage, causing huge delays for many travellers.
The disruption mainly affected passengers who were heading south.
Many of those took to Twitter to vent their frustrations.
Gary Lythgoe tweeted on Tuesday morning: "Cancelled trains, Peterborough trains completely full, kings cross underground limited access. Brilliant."
And Chris Culpin tweeted: "Bet @eastcoastuk customer service is busy today. 4.51am arrival at kings cross only 5 hours 45 min delay for me I was one of the lucky 1's".
On Monday night, Gemma Chandler said: "I've been sitting on a stationary train at Peterborough for 1hr45mins & we haven't had an announcement update for 55mins."
An East Coast spokesman said: "Tickets dated for travel on Monday or Tuesday will be valid for travel on Wednesday and customers are advised to try to travel as close as possible to their original booked time."