PLANNED closures to the Northern Line could bring “untold misery” to passengers, the London Mayor has warned.

Boris Johnson hit out at Tube Lines, the company responsible for the upgrades, after a report by Parliament's Transport Committee said work already done on the Jubilee Line was “unacceptable”.

The line was suspended for 120 weekend days between April 2007 and December 2009, twice as many as expected, and work will only finish in October, ten months passed the deadline.

The committee called on the company to reveal how it intends to stop the same problems blighting its work on the Northern Line.

Mr Johnson said: “I continue to press Tube Lines, and its shareholders, Ferrovial and Bechtel, to revise its hugely disruptive closure plans on the Northern Line.

“Should they proceed as planned, they will be responsible for untold misery for tube users and businesses across the capital.”

The committee also criticised the public private partnership (PPP) contract signed with Tube Lines, saying the risk of taxpayers being forced to shell out money if something goes wrong is too great.

Mr Johnson hailed its verdict as confirmation of a system he had considered flawed for some time.

He said: “This is the latest in a litany of damning verdicts on the PPP, and the failure of Tube Lines to deliver for London.

“This is a system that has wasted hundreds of millions of pounds of public money, yet the Government continues to wash its hands of the mess it has created.”

Andrew Cleaves, Tube Lines acting chief executive, said the company was pleased the committee's report acknowledged it delivered “vital improvements” with a price tag one third cheaper than London Underground.

He said: “As we have always said, it is regrettable that the deadline for completing the Jubilee line upgrade was missed but we are working hard to start carrying passengers on the new system from May.

“Important lessons have been learned and are being incorporated into the Northern line upgrade to speed up work, lower costs and minimise disruption.”