A rail operator running local services in Buckinghamshire has cancelled many Christmas Eve trains and introduced a revised timetable.
Trains on services between London Marylebone, High Wycombe and Aylesbury will also stop running earlier than planned.
"We're continuing to experience problems due to the severe weather," a statement said.
"As a result, we are running a special timetable."
The company warns trains will be cancelled at short notice, there will be delays of up to 60 minutes - especially at peak times - and carriages will be overcrowded.
"Due to a shortage of trains caused by the severe cold, the revised timetable could be subject to short notice cancellations.
"Peak-time trains will be both less frequent and shorter than usual," the company said.
Travellers are advised to contact the train company or consult its website for the latest information.