East Coast train operator LNER is to introduce mandatory seat reservations on all train services from Monday.
The measure, to help social distancing on trains, will mean passengers with flexible tickets will have to pick a service to travel on, in advance.
The company operates services between London and Leeds, and Edinburgh, York, Newcastle and London,
Separately, Avanti West Coast is urging customers to reserve tickets, but has not made it compulsory.
However, it says passengers may not be allowed to get on a train if they do not have a reservation.
Avanti, which runs services linking London, Glasgow, Manchester and Birmingham, is also encouraging people to wear face coverings when they travel.
Chiltern Railways is also advising its passengers to book tickets in advance where possible and to wear masks.
LNER confirmed its shift to mandatory reservations in a tweet.
This contained “tips” for passengers, travelling on its trains, including:
Wear a facemask if you cannot keep your distance
Ignore the seat number on your ticket and choose your own seat
Keep 2 metres apart where possible
One person to a row unless travelling as a household
In standard class leave two empty rows and one in first class
Avoid facing other passengers
The company concluded by asking: “Can you travel another way? Help us keep the trains clear for those who really need them.”