Train passengers face the biggest disruption in decades today because of strike action in a bitter disputes over the role of guards.
Members of the Rail, Maritime and Transport union (RMT) at Arriva Rail North and Merseyrail will stage a 24-hour walk-out today.
Southern, South Western Railway and Greater Anglia will strike on Wednesday and Thursday.
Hundreds of services will be cancelled, replacement buses will be laid on and services that do run will be busier than normal, passengers have been warned.
The union is in dispute over driver-only operated trains, which it claims are unsafe.
Train operator Northern, which operates in South Yorkshire, said: "To help keep you on the move during RMT strike action, we will run more than 1,300 services.
"The majority of available trains will operate between 7am and 7pm as we focus on running as many trains as we can to get you into work and home again. During these hours, Northern will operate around 65 per cent of the normal weekday timetable.
"As the overall number of trains running will be reduced, we do expect trains and any replacement buses we operate to be extremely busy. Please allow extra time for journeys, plan carefully and consider whether travel is necessary."
A Transport Department spokesman said: "The RMT is attempting to disrupt passengers as part of its political game. However, rail companies are keeping passengers moving with the large majority of services running as planned.
"This dispute is not about jobs or safety - employees have been guaranteed jobs and salaries. In fact at Southern Rail, where these changes have already been introduced, there are now more staff on trains.
"The independent rail regulator has said driver-controlled trains, which have been used in this country for more than 30 years, are safe."
Labour has told the five rail operators that the party will halt any future plans to extend driver-only operations if it wins the next general election.
Shadow transport secretary Andy McDonald said in a letter that guards are vital for duties such as helping passengers who need assistance.