The Mayor of London Ken Livingstone has begun another round of legal action against plans to pay private companies to maintain the tube.

The legal challenge is seen as the Mayor's last chance to stop the proposed Public Private Partnership plan (PPP) for the London Underground before contracts are signed.

Mr Livingstone is claiming the scheme will cost London an extra �1.5bn - and the government has not given a commitment to provide the money.

He has asked the courts to hold a judicial review of the planned public-private partnership for the Tube.

Funding gap

The Mayor's office says if the scheme goes ahead fares may have to go up by 25% and there may be rises in London council taxes.

Mr Livingstone said: "Whatever views people have on the merits or demerits of the Public Private Partnership (PPP), I believe that London voters will fully support my efforts to ensure that financial liabilities on this scale are not imposed upon London."

The government says if there is a funding gap it will look into it at a future date.

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.

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.