Mayor of London Ken Livingstone says he will not back down in his fight against the part-privatisation of the Tube.

He has pledged to continue to contest the government's plans to transfer responsibility for the Tube's infrastructure to two private consortia - Metronet and Tube Lines.

On Wednesday Transport Secretary Alistair Darling promised the companies involved nearly �2bn if the controversial PPP scheme collapses because of the mayor's legal challenges.

The government hopes the move will clear the way for the contracts to begin in the New Year.

I will oppose the transfer of this bill to London with every means at my disposal

Ken Livingstone

But the mayor says he will fight the move, which followed his decision to pursue a legal battle over whether the scheme amounted to the kind of state aid outlawed by Europe.

He believes PPP will become a �1.5bn tax burden on Londoners.

He said: "Under this indemnity no significant risk will be borne by the Infracos (the companies running the infrastructure) but a tremendous bill will be landed upon London taxpayers and passengers.

"I will oppose the transfer of this bill to London with every means at my disposal."

Mr Darling had said that he would not let �16bn of "crucial investment" in London Underground be delayed by the mayor's legal challenges.

The two private consortia and London Underground welcomed Mr Darling's announcement.

But the Conservatives wondered if the "squabbling over the Tube" was really over.