The Night Tube is being delayed until after its 12 September launch date as unions continue to threaten strike action.
Sources have told City A.M that London Underground is poised to announce the 24-hour service will miss its start-point next month.
A TfL spokesman said there was "no change to our position", which was that London Underground was "working towards the 12 September" as a launch date. But he acknowledged that it hinged on striking an agreement with the unions, which have so far rejected all deals put to them.
"We are operationally ready, but the launch can't be at any cost," he told City A.M. "We need to get a deal. That is why we have caveated that it can't be at any cost."
The 24-hour service has been at the centre of union disputes for the last few weeks, with a third set of strikes scheduled for a fortnight's time.
RMT has even gone so far as to call for the Night Tube to be suspended, blasting it as “a vanity project”.
There has been a question mark hanging over whether the new service would be ready to launch in time for the deadline, fuelled by mayor Boris Johnson's refusal to commit to the date. On at least two occasions, Johnson has said he was “not too fussed about the start date”.
“I've said we will get it in this autumn, and we shall,” he said last week. “Autumn is not yet upon us... it's still the summer.”
In fact, the launch was so widely expected to be delayed that bookmakers Ladbrokes said it was evens that it would meet the date.
It is not clear whether the delay will affect the impending Tube strike. RMT and TSSA have scheduled two sets of action, on 25 August and 27 August.
Drivers' union Aslef is meeting with TfL bosses later this week in an attempt to find a compromise without striking. Currently Tube drivers are not taking part in the action.
Leader of the London Assembly Labour group Len Duvall said: “By speculatively announcing a start date without any consultation with the people expected to run the service Boris Johnson’s gung-ho approach has led to disputes, disruption and now delay.
“It’s been clear for a long time that the problems facing the night tube would not be easily overcome so in a sense a delay isn’t a major surprise. I hope this delay will provide the breathing space necessary for unions and management to sit down and negotiate a resolution to this dispute without the need for further disruption to passengers.
“From the outset Boris Johnson has treated the Night Tube as more of a publicity stunt despite it being a deeply complex project.”