A TUBE upgrade which led to misery for commuters has been slammed as a 'fiasco' after losing travel chiefs millions in ticket revenue.

The upgrade to the Jubilee Line, which serves North Greenwich and The O2, may not be completed until 2011 - four years after work began.

It was originally set to be completed last December but work has dragged on and weekend closures are a regular occurrence.

In response to questions by leader of the Liberal Democrat London Assembly Group Caroline Pidgeon, Mayor of London Boris Johnson conceded the work meant from £10m to £12m in lost ticket revenue.

The upgrade was being carried out by the Tube Lines company, now a subsidiary of Transport for London (TfL), with the aim of increasing line capacity by 45 per cent.

Mr Johnson said: “Since acquiring Tube Lines in June 2010, TfL has been working urgently to determine the full state of all Tube Lines’ upgrades programmes and in particular their delayed upgrade of the Jubilee line.”

But Ms Pidgeon said: “The upgrade of the Jubilee Line has turned out to be a case study in exactly how not to upgrade the tube.

“There is now overwhelming evidence that carefully planned blockades of short sections of the tube for two or three weeks would be a far better way to upgrade the tube than the expensive fiasco of literally years and years of weekend closures.”