There have been severe delays on the Northern Line

An LU report found that Metronet's renewal programme had been unsuccessful and District Line track had not been maintained to the relevant standards.

Tube Lines also failed to improve Northern Line performance, it said.

Metronet said progress had been made but there was still much to do. Tube Lines said "robust improvement programmes are being moved forward".

Speed restrictions

The report was the third annual review of the private public partnership (PPP) which was agreed in December 2002.

It identified that Metronet had failed to properly prepare sections of track ahead of the summer heatwave resulting in "a series of disruptive speed restrictions".

Also it highlighted that Metronet's station renewal programme was well behind schedule, with only 14 out of a scheduled 35 projects delivered - all of which were late.

The Northern line continues to be a challenge and ... we too are disappointed and frustrated by the slow progress being made with its reliability Tube Lines

The report said with regard to renewal projects "the Infracos (infrastructure companies), particularly Tube Lines, have demonstrated the ability to deliver, on time and on budget".

But LU's Tim O'Toole said: "Nonetheless, Metronet and Tube Lines continue to disappoint in many respects and failed to meet the two key challenges I laid down in last year's report.

"All parties involved in the renewal of the Tube must commit to delivering improvement at a faster rate than we have seen so far."

Slow progress

Under the 30-year PPP contracts, the infracos are responsible for the maintenance and renewal of rolling stock, stations, track, tunnels and signals.

A spokesman for Metronet said: "A lot of progress has been made in the last year and passengers are already benefiting from these improvements.

"We are doing all we can to catch up on our stations programme and are agreeing a plan with London Underground to get this back on track."

A Tube Lines spokeswoman said: "The Northern line continues to be a challenge and... we too are disappointed and frustrated by the slow progress being made with its reliability."