Southern Railway guards are to stage a fresh strike in their long-running dispute over staffing, threatening more chaos for hundreds of thousands of passengers.

Members of the Rail, Maritime and Transport (RMT) union will walk out for 24 hours on January 23, the day before drivers go on strike again in protest at driver-only trains.

RMT members have staged dozens of strikes after Southern changed the role of guards, with the union complaining safety was being compromised.

Southern train services continued to be disrupted on Thursday by an overtime ban by Aslef, the train drivers’ union, even though drivers returned to work after a 48-hour strike.

Another drivers' strike will be held on Friday and again for three days later in the month. Southern has warned there will be no services on Friday because of the strike.

RMT leader Mick Cash said Charles Horton, chief executive Govia Thameslink Railway (GTR), had promised earlier this week to retain a second safety-critical member of staff on trains.

But he said pledge by GTR, Southern’s parent company, repeatedly "melts away" during direct talks.

Mr Cash said: "That is the main reason why we are forced again to put on further strike action.

“It is down to the company to end this posturing and to get back into the room with us to kick-start the negotiating process which is what the public are clearly crying out for.

"There is a golden opportunity between now and the next phase of action to get serious and genuine talks under way.

"RMT is available but it is down to Southern/GTR to show that same commitment and to stick to the promises they gave on camera in front of a TV audience across the region.”

Responding to the RMT's latest strike date announcement, a Southern spokesman said: "Charles [Horton] invited the RMT to fresh talks but we’ve had no dates or times from them.  

"We’d also point out that on the morning of 14 December, our chief operating officer personally invited Mick Cash for talks with him later that day.

"Mr Cash did not show up. So the union are once again being disingenuous."

“These strikes are not about safety; it’s purely about the unions trying to turn the clock back, hang on to outmoded working practices, which technology now eradicates, and union power.

"We need to modernise our trains and the services passengers want.

"Every train that previously had a conductor before 1 January now has either a conductor or a safety-competent on-board supervisor rostered to work.  We need to end these strikes and end them now.”

GTR is taking fresh legal action against Aslef by going to the Supreme Court to try to stop the strikes, after losing a court case and an appeal last year.

A statement said: "GTR is determined to protect its passengers and its business from unlawful industrial action.

"GTR is therefore prepared to continue its legal claim to the Supreme Court, as it believes that it has an arguable case that the industrial action is unlawful under EU law."

Last month, the High Court rejected an argument from GTR that industrial action would breach customers' rights.

Aslef described last month's legal action as a waste of taxpayers', shareholders' and passengers' money.

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