Train companies will operate a reduced service from Monday in order to provide a more reliable service for key worker "heroes" such as emergency services and healthcare professionals.
The Department of Transport said core services will still run, ensuring people can travel to medical appointments and to allow vital goods - food and fuel - to be shipped around the country where needed.
The changes come after the Government issued guidelines warning against all but essential travel as the Covid-19 pandemic continues.
Robert Nisbet, director of nations and regions at the Rail Delivery Group, which represents train operators and Network Rail, said the measures are being taken in a time of "extraordinary national challenge".
"This is not a decision we take lightly," he said.
However, implementing these measures now will mean that we can continue to operate trains over a prolonged period with fewer railway workers, who like so many others are to be commended for putting the needs of the country first, and whose safety remains front of mind.
Mr Nisbet said the group would be monitoring demand for services closely in the weeks ahead and would adjust timetables accordingly.
The Department of Transport said it intends to reduce the services gradually over the coming days to minimise disruption.
We are taking decisive action to protect the public, which means reducing travel for the time being, whilst still ensuring keyworker heroes can get to their jobs to keep this nation running. For passengers in crucial roles, including essential workers in our emergency services and NHS, alongside people who need to attend medical appointments or care for loved ones, these changes protect the services they rely on. Our railways are at the heart of this country's transport links, and we continue to work closely with the industry to develop measures that protect operators in these challenging times.
South Western Railway acknowledged that it is "a difficult time" for passengers but urged people to follow official advice.