The computer system is so sensitive it is picking up safety faults that do not exist. The latest hold-up on Friday closed part of the line for hours. Unless the system is sorted out by New Year it will cause chaos as visitors to the Millennium Dome find alternative routes.
The line is crucial to City banks such as HSBC and Citigroup, who are moving to London Docklands, bringing in another 50,000 commuters.
The problems follow last week's announcement by Railtrack that it had shelved its modern signalling for the pounds 3bn West Coast Main Line upgrade.
The JLE system, designed by Westinghouse, is unique as it "reads" information from computers installed across the network. If it finds something it does not understand it turns all signals from green to red.
Tube managers are understood to be furious that they are being blamed for the delays. A source said: "We are tearing our hair out, and a lot of it is to do with Westinghouse. Our guys are busting a gut to get it sorted." But JLE bosses denied they were unhappy with Westinghouse, and said they were confident the system would be fully functional by New Year.
Cliff Mumm, senior vice-president of Bechtel, the US engineer brought in last year to get the line finished, said: "It is a new system and is over-responsive, but in the interests of safety. Westinghouse is being incredibly responsive."
The JLE is now open between Stratford and Waterloo. Mr Mumm admitted there would be more shutdowns when it is linked to the Jubilee Line at Green Park next week.Reuse content