The union has called on the Government to end the “shocking waste of public money” and hasten the return of Metronet contracts to the public sector.

RMT urged ministers to end uncertainty over the future of essential Tube upgrades and lift the shadow of insecurity from thousands of essential infrastructure workers by acting to end delays to Transport for London's takeover of Metronet's contracts.

Protracted delays, including wrangling over contracts awarded by Metronet to its own shareholders, have meant that the target date of January 18 for getting the contracts back into the public sector under direct Transport for London control has been missed.

The government has estimated that the first six months of administration, from July 18 last year, cost £345.5 million.

With another £14.4 million being swallowed every week, the extra cost will pass £500 million if the Metronet contracts remain in administration on April 2.

"The long and the short of it is that the privateers who walked away from Metronet are still draining tens of millions in public money out of the Tube network," RMT general secretary Bob Crow said today.

"It is scandalous that the same shareholders who walked away from Metronet when they couldn't squeeze even more money out of the public purse are still raking in handsome profits out of contracts they effectively awarded themselves, " said Bob Crow the RMT general secretary.