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The first ever strikes on Night Tube are to take place on two Saturday nights next month, the Evening Standard can reveal.

Train drivers will walk out on the Saturday nights of April 8 and April 29.

The move will dismay business leaders who look on Night Tube as the key to regeneration of the capital’s weekend night life.

More strikes are not ruled out if the bitter dispute about how the 24-hour operation – which began last August, almost a year late – is staffed.

The Aslef union, which represents about three quarters of the Night Tube drivers, will declare the result of its strike ballot tomorrow (Thurs) lunchtime.

Voting is forecast heavily to endorse industrial action. Immediately after the result the union’s executive committee will announce the strike dates.

Aslef declined to comment in advance of the result.

Night Tube operates on the Central, Victoria, Northern, Jubilee and Piccadilly lines. A walkout by Aslef members would halt all or the vast majority of services.

Aslef has deliberately given more than the required seven days legal notice of industrial action to allow time for talks to take place with Tube management.

The move follows the announcement yesterday by the rival union RMT that its driver members had voted to support strike action.

The union’s controlling executive committee is now considering the next move, including the strike option. They could even order walkouts to take place before the Aslef strikes.

The unions say as a result of a “ blatantly discriminatory policy” Night Tube train operators have been prevented from moving into vacant full-time positions for a period of at least 18 months.

A Night Tube driver is contracted to 16 hours a week.

Train drivers are normally drawn from the wider workforce. But part timers have been barred from moving into full-time vacancies for the first 18 months – but part time station staff can apply.

Finn Brennan, Aslef’s London Underground district organiser, said: “The vast majority of Night Tube drivers took up the job because they saw it as a stepping stone to a full-time train driver’s job.

“They believed LU’s assurances that they would have opportunities to progress, not to just spend year after year working every Friday and Saturday night.”

RMT General Secretary Mick Cash said: “It is outrageous that London Underground have decided to discriminate against their Night Tube drivers.

"This is a senseless and damaging policy that picks out one group of staff for negative treatment and of course the drivers are angry and that is why our members have voted overwhelmingly for action. That ballot result will now be considered by RMT’s Executive.”

“RMT would call on LU to see sense, stop these stupid attacks on career progression and fair reward for overtime working and confirm that this discrimination against the Night Tube drivers has been lifted.”

Peter McNaught, operations director for London Underground, said: “Night Tube services have been running since August last year in line with agreements reached with the unions.

"We’ve met with the unions to discuss and resolve the new issues that they have.

"We have invited the unions to more talks this week and I encourage them to continue discussions with us rather than threaten industrial action.”