The strikes were called after the company and its administrator failed to give the unequivocal guarantees on jobs, transfers and pensions that the union is seeking.

"The letter we have received from Metronet and the administrator falls way short of the guarantees our members need and deserve," RMT general secretary Bob Crow said today

"What we sought was firm, unequivocal guarantees, but frankly our members are being asked to stake their jobs and their pensions on a pig in a poke.

"The only assurances we have received about jobs and transfers cover only the period of administration, and that is simply not good enough.

"It is strange that the administrator can determine all sorts of things about the future of the PPP contracts, apparently including who the next fat-cat privateer might be, but is not in a position to give on-going guarantees on the jobs of the people who actually do the work.

"On pensions we have received no guarantee from the employer at all.

"When the government forced through the disastrous part-privatisation of the Tube, the deputy prime minister told the world that the pensions of our members would be safe.

"What we need from the administrator and Metronet is an unequivocal confirmation that Prescott's statement will be adhered to by this employer or by any other employer under the PPP. Anything less is unacceptable.

"Of course we welcome Ken Livingstone's desire to bring Tube maintenance back in-house, but the fact remains that the guarantees we need can only come from the employer.

"When the jobs and pensions of our members are at stake - not to mention the Tube upgrades that the capital cannot do without - vague assurances are not enough, and the strike by our members will go ahead at 6pm on Monday," Bob Crow said.