The Rail Maritime and Transport (RMT) union said Metronet had agreed not to transfer workers to Bombardier, one of the companies in the consortium.

Up to 2,000 union members had been due to walk out from 6pm on Sunday, threatening travel chaos for millions of Tube users.

Talks aimed at ending the dispute had "collapsed" earlier in the day, but less than two hours later, the RMT announced it was suspending the action.

The RMT said that Metronet, which maintains two thirds of the Tube system, had withdrawn plans to transfer workers to other companies.

"In a dramatic about-turn, Metronet informed RMT .. that posts and individuals it intended to transfer to Bombardier would now remain in-house, and that it would not bring forward any further plans for outsourcing," said a union spokesman.

General secretary Bob Crow said: "This is the sensible outcome we fought for from the start, and it means quite simply that there will be no outsourcing of our Metronet members' jobs.

"Our Metronet members deserve congratulating for standing solidly together to defend their organisation, jobs and conditions and to prevent further dangerous fragmentation.

"Their stand, in the face of hostile media attention, has been vindicated by the outcome of this dispute."

The union added that Metronet had also agreed to hold talks aimed at bringing cleaning contracts back in-house.