It has been a long, hard slog to get where we are

Paul Godier London Underground

But rail unions said the Public Private Partnership plan (PPP) would be "an unmitigated disaster".

Mick Rix, general secretary of the train drivers' union Aslef, said: "Passengers and the taxpayer will be paying for this blunder for years to come and before very long we will have to work out how to undo the PPP and restore a publicly controlled underground."

This stage in the Tube's PPP can be likened to an exchange of contracts in the housebuying process.

It came about after London Transport Board voted unanimously to proceed with the modernisation plans.

Mr Godier said: "It has been a long, hard slog to get where we are today.

Investment

"We are all working flat out to make sure the final pieces of the jigsaw are in place so that work can start, without further delay, to deliver a world-class Tube for a world-class city."

Transport secretary Stephen Byers said he shared LT's views that the plans, which will see around �16bn invested in the Underground over the next 15 years, were "the right solution and offered significant benefits for Londoners".

Under PPP, the Tube Lines consortium will be responsible for maintaining and upgrading the Jubilee, Northern and Piccadilly lines of the Tube, while the Metronet consortium maintains the rest of the lines.

It will cost the taxpayer and commuter a packet

Bob Crow RMT

The actual operation of the trains will stay in the public sector and will be the responsibility of the London Mayor and the capital's Transport Commissioner.

Mayor Ken Livingstone and the commissioner Bob Kiley have both been bitterly opposed to PPP.

Bob Crow, general secretary of the Rail Maritime and Transport union, said: "The disaster of British Rail privatisation is being exported wholesale on to London Underground.

"Londoners don't want it, our members on the Tube don't want it and the Mayor doesn't want it.

"The only people who want this to happen, apart from the government, are the privateers dribbling at the prospect of getting their snouts stuck into another trough."