More than 20 Christmas Eve mainline trains have been cancelled on the line between London and Norfolk, through Hertfordshire and Cambridgeshire.
A revised timetable is also operating on the Thameslink line between Bedford and St Pancras International.
First Capital Connect blamed the weather for timetable revisions.
"Great Northern routes are running a revised service to reflect the recent impact of the weather on our train fleet," a statement said.
"London Underground, National Express East Anglia and East Midland Trains are accepting First Capital Connect tickets."
Commuter and local service trains on routes within London and north of Potters bar are also disrupted with a revised timetable showing many other cancellations.
The company had warned earlier in December that trains on its Great Northern route would stop at 2200 GMT on Christmas Eve.
Travellers are asked to contact the company or refer to their website for the most up to date information.
There are no services on Christmas Day.