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The Tube strike scheduled to start on Wednesday afternoon appears set to go ahead after union bosses today said they were “increasingly pessimistic” a deal could be struck.

Transport for London warned there will be no trains at all from late afternoon Wednesday or all day Thursday.

The 24-hour walkouts by members of four unions will take place from 6.30pm but services will start to wind down before then.

Union bosses were meeting London Underground management at Acas, the conciliation service, today and possibly tomorrow but feared little chance of a deal in the twin dispute over operation of the Night Tube and annual pay.

They said the issue of Night Tubes, due to start running in September, was the principal sticking point, warning that even if LU made a slight increase to the annual pay offer it would not be enough for the strike to be called off.

Finn Brennan, the district secretary of Aslef, which represents the majority of train drivers, said he is “increasingly pessimistic” that an agreement would be reached. He accused Tube chiefs of having “wasted the window of opportunity to try and reach agreement”.

“They have not moved their position at all during the last three months and seem intent of forcing through change without negotiation,” he added. Mr Brennan said the dispute was not about pay but achieving a “work/life balance” for operating the Night Tube.

Steve Griffiths, LU’s chief operating officer, said: “Londoners and businesses overwhelmingly back the Night Tube.

“Most of our staff will not be affected by the new services at all because it affects only five of eleven lines. Some staff will actually work fewer nights than they do now because we have hired 137 more train operators specifically for the Night Tube.

“The train staff who will be affected are being asked to work around an additional seven nights each year on average, with no increase in their total current hours.

“In return, we are offering a realistic pay increase this year and next, as well as an additional payment for Night Tube working. We are ready to negotiate, but any increase must be sustainable and fair. I urge the trade unions to keep talking to us.”

First Great Western services to and from Paddington also face disruption from Wednesday evening due to a 48-hour strike by RMT members in a separate dispute over working conditions.