Train passengers have been urged to only travel if absolutely necessary as rail workers are rset to walk out as part of nationwide industrial action.

Fewer trains will run on Southern, Thameslink and Gatwick Express services, with several stations in Sussex likely to have no services at all.

Trains will also start later each day, from 7.30am, and finish earlier than normal - as early as 4.30pm.

Govia Thameslink Railway (GTR), which operates the services, said that services will also be disrupted the day after strike action, with trains starting later in the day.

The rail firm has warned customers that the first and last trains of the day will be particularly busy, urging people to consider leaving later or returning earlier if possible as no alternative transport will be available.

RMT workers will join workers across several industries as strikes escalate over the next few weeks.

Angie Doll, chief operating officer for GTR, said: “We’re really sorry for the enormous inconvenience this RMT action will cause to all of our customers during next week’s two 48-hour strikes.

“Regrettably, we are asking customers to travel only if absolutely necessary, and check service information for their local station as some routes won’t have trains at all.

“We understand how next week’s strikes and the uncertainty caused by the ensuing industrial action will be incredibly difficult for customers, particularly over the festive and New Year period.

“We don’t want our customers to get caught out and urge you to plan ahead and make alternative travel arrangements if necessary.”

Rail union leaders have continued to blame the government for “blocking” a deal to end the long-running dispute over pay, jobs and conditions which threatens more travel chaos in the run-up to Christmas.

Train services between December 13 and December 17 will face disruption due to strike action, with further walk-outs planned from December 24 to December 27 and January 3 and January 7.

An overtime ban across the railway network will also affect services between December 18 and January 2, with trains expected to be extremely limited.