A consortium of private sector firms which will fund repairs and refurbishments on part of the London Underground has outlined its plans in more detail.

The consortium, known as Tube Lines, will spend about �4.4bn upgrading three lines of the ageing network over the next seven-and-a-half years.

Under a deal signed with the government, it will upgrade the Jubilee, Northern and Piccadilly lines in return for guaranteed revenue over the next 30 years.

Tube Lines has raised �2.1m and the rest will come from government funding or fares.

For the first time London Underground can think long term and bring about a sustainable improvement in performance Terry Morgan, managing director Tube Lines

The consortium says its top priority is to improve reliability and it aims to cut delays by 10% within 12 months.

Tube Lines plans to replace signalling systems on the Jubilee and Northern lines by 2011, and improve 97 stations across the three lines.

The Jubilee Line will also get 59 extra carriages - allowing each train to have seven cars instead of six.

Tube Lines Managing Director Terry Morgan said the consortium faced an enormous challenge.

"We're dealing with an Underground system that has had decades of underinvestment.

"It's one that, clearly as we bring private sector funding into play, means for the first time London Underground can think long term and bring about a sustainable improvement in performance."

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.

The scheme has been strongly opposed by London's Mayor, Ken Livingstone, and by transport workers' unions.