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Tube unions have been urged to call off a planned 24-hour strike which would bring severe disruption.

Up to 4,000 station and ticket staff are set to walk out from 6pm on Sunday in a dispute over staffing numbers.

London Underground is preparing contingency measures if the strike goes ahead, which could see many stations shut and some lines partially closed.

The walkout — and the threat of more to come — is in protest at 800 job cuts and the closure of ticket offices under former mayor Boris Johnson’s regime as a cash-saving measure.

The unions are furious with Mayor Sadiq Khan for not reopening at least some central London ticket offices.

Brian Woodhead, LU operations director, said: “We have always committed to reviewing our new staffing model with the trade unions during its first year. We are recruiting additional staff for stations and believe this will help us to provide a better service.

“We will continue working with the unions, as well as implementing recommendations made by the London TravelWatch review, to ensure our customers feel safe, fully supported and able to access the right assistance at all times.

"We encourage the unions to work with us on this process rather than threatening strike action.”

Discussions between both sides at conciliation service Acas broke up on Wednesday without agreement and talks were due to restart on Thursday.

Mick Cash, the RMT leader, said the strike “remains on. The ball remains in LU’s court and while the RMT remains available for talks it is down to the company to come back into the process with serious proposals.”

Manuel Cortes, leader of the TSSA union which represents ticket office staff, said: “It doesn’t appear that LU is serious about resolving this dispute. Their complete lack of urgency tells its own story.

“We need a significant increase in staff numbers, in the hundreds, just to be back in a position where our Tube can operate safely and where station closures are no longer the norm.”