Union leaders were under pressure tonight to call off the London Underground strike after it emerged new peace talks would take place on Friday.
Four million tube users have faced a day of disruption and frustration at the start of a 48-hour walkout by members of the TSSA and RMT.
Union leaders insisted the strike was "rock solid" but LU managers claimed a third of all trains were running.
Tonight the conciliation service ACAS announced the two sides in the dispute have been invited to new talks on Friday.
London Underground Managing Director Mike Brown said: "We welcome further talks, and the unions' decision to return to ACAS, but why wait till Friday?
"I call on the leaderships of the RMT and TSSA to meet us tomorrow and to suspend Thursday's strike so we can get on with talks to resolve this issue and avoid any more unecessary disruption to Londoners."