The September 12 start date for London Underground's new all-night Tube service is expected to be delayed, according to sources.
The development came as London Underground drivers confirmed they would not be joining two fresh strikes later this month over the night Tube dispute.
Sources at the Aslef union said further talks will be held in a bid to resolve the long-running row.
Members of three other unions are still due to stage two 24-hour walkouts from the evening of August 25 and 27 following two stoppages in the past month.
Talks were held today at the conciliation service Acas in a bid to break the deadlocked row.
Aslef held off making any announcement on strikes until today's resumed talks, and sources said it had been decided the union would not be taking part in the new stoppages.