RMT general secretary Bob Crow today wrote to Ms Kelly and Mr Livingstone seeking meetings and "urgent confirmation" that thousands of Metronet workers' jobs would be secure and that the maintenance and renewal of the Underground would not be compromised.

"The maintenance and renewal of two thirds of the London Underground has been thrown into doubt and it is clear that the Metronet contract is no longer tenable," Bob Crow said today.

"Very few people will shed any tears if Metronet goes to the wall, but in its death throes it should not be allowed to decimate the skilled workforce that will be needed long after the company is forgotten.

"We agree with the Mayor that London Underground can take over Metronet's functions, and it has always been our view that it would be far more economic and efficient for Tube infrastructure work to be in-house, under the direct control of LUL.

"If a failing privateer goes into administration it should not be passengers who pay through increased fares or the scaling back of upgrades the tube desperately needs, nor should the workforce have to pay the price through attacks on jobs and conditions," Bob Crow said.