A consortium of private sector firms has signed a landmark deal with the British government to upgrade part of the London Underground.

Under the deal, the consortium will fund repairs and refurbishments on the Underground's Jubilee, Northern and Piccadilly lines in return for a guaranteed revenue stream over the next 30 years.

The consortium, known as Tube Lines, will spend about �16bn ($25.8bn) upgrading the ageing Underground network over the next 15 years.

Work is set to begin immediately in the New Year.

"For passengers, the first improvements to be witnessed will be a reduction in the number of delays and a substantial improvement in the cleanliness of the trains and stations," said Tube Lines chief executive Terry Morgan.

Targets

Tube Lines aims cut delays by 10% within 12 months, and is planning to install new signalling systems on the Jubilee and Northern lines by 2011.

The contract is part of a government initiative to encourage private sector participation in the construction and maintenance of public service facilities.

Extending the scheme to the London Underground has been fiercely opposed by London's Mayor, Ken Livingstone, and by transport workers' unions.

Mr Livingstone said "My approach will be to do everything in my power to extract the best and safest possible service for London.

"But the Government has retained control of the Tube in order to impose this experiment on London and the Government remains responsible for all of the consequences."

The consortium consists of UK outsourcing firms Amey and Jarvis, and US engineering giant Bechtel.

The deal was originally due to have been signed in late November, but was delayed by one month, partly because Amey ran into financial difficulties.

A second consortium of private sector firms, Metronet, is due to take over responsibility for the remainder of the London Underground network in the spring of 2003.