Mr Justice Sullivan said there were "powerful arguments" which suggested the industrial action by the Rail Maritime and Transport union was unlawful.

The BBC's Amanda Harper: "The RMT has vowed to fight on"

The RMT had called its 7,000 tube members out for two 24-hour strikes starting at 1100 GMT on New Year's Eve and again from 1900 GMT on 3 January in a row over job security.

They are concerned about employment conditions under plans to inject private money into the tube system.

The action had threatened to disrupt New Year celebrations and the return to work for many commuters.

The union has agreed to comply with the order, subject to any appeal, and is sending letters to its members.

Union critical

The union's assistant general secretary, Bob Crow, was critical of London Underground's approach.

He said: "They spend more time in the courts than they do round the table negotiating. This has put a further barrier in front of industrial relations working properly on the underground."

But the director of human resources for London Transport, Ann Burfutt, said there had been no breakdown in negotiations and another meeting was lined up for 5 January.

She said: "We are relieved that people are going to be able to enjoy the New Year and be able to return to work on 4 January."

The RMT balloted its members in the summer and held two strikes in June and July.

It believed it had the legal authority to call further strikes without holding another ballot because negotiations have been continuing.