Train bosses are warning passengers to travel only if “absolutely necessary” as strike action will cause disruption well into the new year.

People planning to use key Sussex operators are being told to avoid travelling on Christmas Eve, when trains will stop running as early as noon because of national RMT strike action.

Govia Thameslink Railway, the operator in charge of Southern, Thameslink and Gatwick Express, has strongly advised people who have no choice but to travel to check their whole journey.

Trains do not normally run on Christmas Day or Boxing Day and they will not resume until as late as midday the day after, on December 27.

Passengers travelling that day are advised to “check train times carefully and plan ahead”.

Due to strike action, passengers are also told to expect late-notice changes and cancellations to services from now until  January 2.

There will be more RMT national strikes at Network Rail on January 3, 4, 6 and 7.

This means there will be limited services, late starts and early finishes on these days.

On days after these strikes, January 5 and 8, services will restart later, at around 7.30am.

 “We’re really sorry for the disruption this ongoing RMT action will cause our customers over the entire festive period, until January 8,” said Angie Doll, chief operating officer at GTR.

“We urge our customers not to travel unless absolutely necessary on Christmas Eve, as services will finish much earlier than usual across the country, with last trains departing at around 12pm on many of our routes.

“Trains won’t restart until as late as midday on December 27. We understand this is going to make life difficult for many, and urge you to make alternative arrangements if you must travel.

“Unfortunately, trains may also be subject to late-notice change on non-strike days, due to a national overtime ban. Therefore our strong advice is to always check your journey before setting off, allow extra time for travel and don’t wait to catch the last train home if possible.”