The Mayor of London's legal challenge over government plans to part privatise the Tube was a "waste of public money", according to the London Assembly.

Assembly transport committee chairman John Biggs said Ken Livingstone and transport commissioner Bob Kiley used the courts because they had lost the political argument.

But Mr Livingstone has defended the action against the Government saying he was trying to save public money.

He told BBC London the public-private partnership (PPP) was a bad deal that would lead to higher Tube fares or higher council taxes.

They have lost the political argument

John Biggs, London Assembly transport committee

The case was abandoned during the hearing because lawyers said Mr Livingstone and Mr Kiley had little chance of success.

Mr Livingstone agreed to pay up to �4m towards costs.

On Tuesday he told BBC London the cost was justified.

"The gap between the money the government is giving us and what we have to pay contractors is �1.5bn over seven years," said Mr Livingstone.

"That is a 25% fare increase on Tube fares or �1.20-a-week increase on the council tax.

'Difficult case'

"That is such a bad deal that even with the high cost of the court case it was worth taking the chance if we could save Londoners that money."

He and Mr Kiley had been seeking a judicial review of the government's PPP plans for the Tube.

Mr Biggs now says he plans to ask the Audit Commission to investigate whether Mr Livingstone and TfL used "reasonable advice or acted recklessly with public money" to pursue a case that had a "slight" chance of success.

Mr Biggs said: "It seems to be a waste of public money. They have lost the political argument and seemed to be using the courts for some sort of argument against the Government.

'Full backing'

"The least we could have expected was a basic statement about what went wrong and what happens next".

A TfL spokeswoman said: "We had the full backing of the board to proceed with the action.

"We will comply with any investigation of the Audit Commission if they want to look at it."

The government hopes PPP will bring a �16bn investment in the London Underground.