Tony Blair is preparing to push ahead with the Government's controversial plans to give control of London Underground to commercial companies after assurances that the move will be safe and offer value for money.

The Prime Minister and Stephen Byers, the Secretary of State for Transport, are preparing to launch a "great debate" next month on the merits of the public-private partnership (PPP) over Ken Livingstone's rival plans for the Tube, The Independent has learnt. They will attend "road show" meetings with Labour Party members in London from 8 February until 20 March, when a final decision on the scheme will be announced.

Crucially, ministers are seriously concerned that if the PPP fails in any way it would deter the £40bn of private investment the Government is relying on for its 10-year plan for the railways. Treasury officials are also worried it would send the wrong signal to the City at a time when the private sector is being invited into parts of the health service and the education system.

Ministers have in recent months allowed themselves an escape route from the plans by suggesting the Tube will be handed over to the Mayor of London if they do not pass safety and cost tests by Ernst and Young and PricewaterhouseCoopers respectively.

However, with final bids from the private sector now submitted, London Underground is convinced its revised contracts will pass both tests and ministers are "very confident" the scheme will go ahead intact.

The Department for Transport, Local Government and the Regions began to worry late last year about the rising costs of the three contracts to run separate parts of the Underground trains and track.

London Underground sources have revealed that the PwC audit has found no serious problems and that the value for money and safety tests have been met.