Tube passengers are still waiting for improvements, the Lib Dems said

Tube Lines, responsible for the Jubilee, Northern and Piccadilly Lines, was fined the most at �24.32m.

The Liberal Democrats said PPP firms are "failing miserably" at delivering.

Tube Lines said it has hit its targets on the Jubilee and Piccadilly Lines and reliability is improving overall. Metronet paid out �2m.

The maintenance of the Tube was privatised under the controversial Public Private Partnership (PPP) scheme in 2003.

As London's most heavily used and oldest Tube line the Northern Line Terry Morgan Tube Lines

Metronet and Tube Lines were given 30-year contracts worth �15bn to improve the ageing underground network.

Tube Lines chief executive Terry Morgan recognised that service on the Northern Line had "fallen short of expectations".

He said: "Our progress in cutting delays on the Jubilee and Piccadilly lines reflects the fantastic effort put in by our people at the front line to turn around the performance of an ageing and outdated system.

"However as London's most heavily used and oldest Tube line, the Northern Line has proved more challenging and more problematic."

'Failing miserably'

He added that more money was being spent on the Northern Line to meet the challenge.

The figures were revealed in a question to the mayor by the Lib Dems.

They showed that one arm of Metronet called BCV, responsible for the Bakerloo, Central, Victoria and Waterloo and City lines, was fined �11.31m.

But the other arm Metronet SSL, which maintains the remaining lines, was awarded �9.10m in bonuses.

Lib Dem London Assembly member Geoff Pope said: "The Tube maintenance firms are failing miserably to deliver on the pledged improvements for the underground."

He said Tube maintenance should be brought back in house.