Only about 20% of normal train services will run on Saturday due to another strike by workers, Network Rail said.
Around half of the network will be closed all day and trains will only operate between 7.30am and 6.30pm.
Passengers are being urged to “only travel by train if absolutely necessary”.
More than 40,000 members of the Rail, Maritime and Transport (RMT) union at Network Rail and 15 train operating companies will walk out on Saturday in a row over jobs, pay and conditions.
Services will start later than normal on Sunday morning as workers return to duties.
Tim Shoveller, Network Rail’s chief negotiator, said: “Despite our best efforts to compromise and find a breakthrough in talks, rail unions remain intent on continuing and co-ordinating their strike action.
“This means railway staff forgo even more of their pay unnecessarily, passengers’ lives are disrupted once again and the railway’s recovery from the pandemic is further damaged.
“We’re asking passengers who want to travel this Saturday to only do so if absolutely necessary.
“Those who must travel should expect disruption and make sure they check when their last train will depart.”
Daniel Mann, director of industry operations at the Rail Delivery Group, which represents rail companies, said: “These strikes continue to disrupt leisure travellers, shift workers and undermine the many businesses who are struggling with rising costs and reduced footfall.
“Further action by the RMT and TSSA (Transport Salaried Staffs’ Association) leadership will only damage the railway’s recovery from the Covid-19 pandemic.
“We want to give our people a pay rise, but we need the leadership of trade unions to make a commitment to reform, which is how we can improve services and deliver a fair deal for our people, passengers and for taxpayers.”
Passengers are advised to check National Rail Enquiries or their train operator’s website for updates.
People with a ticket for Saturday whose journey is cancelled or rescheduled are entitled to a refund.
Alternatively, they can travel either on Friday or another day up to and including Tuesday October 11.
Season ticket holders are entitled to compensation through the delay repay scheme.