More than 40,000 Rail, Maritime and Transport union members at 15 train operating companies and Network Rail are striking.
The action is part of an ongoing row over jobs, pay and conditions.
Services will start later and finish earlier and people are urged to avoid travelling unless absolutely necessary.
Members of the TSSA union, who staff station ticket offices and work in on-board operational roles, will also strike, affecting Avanti West Coast, c2c and Transpennine Express services.
About half of the rail network will be closed all day and trains will operate only between 07:30 and 18.30 BST, with services on Sunday also starting later than normal as workers return to duties.
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