Railway companies advise people to avoid non-essential travel after recording an increase in travel planning of almost a quarter.
Rail services will be increased from approximately 50% of the normal timetable to 70% from Monday as part of the relaxation of the restrictions of the coronavirus lock.
But there are fears that distance measures may not be possible due to the number of passengers.
The industry supplier, the Rail Delivery Group (RDG), said 3.7 million trips were planned between Sunday and Thursday, compared to three million in the same period a week earlier.
Passengers are asked to drive, cycle or walk to their destination rather than by public transport.
The capacity of trains is limited to 10 percent of the normal number of passengers, the RDG warns. Those who have no alternative way of making their journey are asked to avoid peak times.
People embarking on long journeys are “strongly advised” to reserve a seat or they may not be allowed to travel.
Countries and regions director Robert Nisbet said, “To keep people safe, there will only be one-tenth of the usual number of people on the train, even though train companies will gradually expand their services next week.
“We need people’s help to keep trains free for those who really need them, so we ask people to consider alternatives such as cycling or walking, and if not, to travel at quieter times.
“We are committed to keeping passengers and staff safe, including cleaning trains and stations several times a day, managing capacity and increasing signage to help people move.
“For those who do need to take the train, we ask that they plan ahead, consider others and remain safe when using public transport.
“That means you need to buy tickets online for quieter times of the day, where possible to distance yourself from society, wear a face covering and keep your hands clean.”
Transport companies are urged by the government to rearrange, remove or restrict the seats “to try to ensure that social distance is respected”.
This can include blocking chairs around others and removing face-to-face chairs.