Tube unions order eight days of strikes starting next week

The action will cripple services on three of the busiest lines - the Jubilee, Northern and Piccadilly - used by nearly two million people a day.

Other lines could also suffer major disruption because of the knock-on effect.

RMT leaders announced two 72-hour stoppages - starting next Wednesday - among 1,000 engineers and frontline staff employed by Tube Lines.

The union is in dispute with the private sector consortium responsible for the three lines over pay and pensions.

RMT members are angry they have not been offered a pay rise to match the 5.1 per cent awarded to staff at Metronet, the failed consortium taken over by London Underground.

Bob Crow, the RMT leader, said members had voted "overwhelmingly" to back the strike and refused to rule out further stoppages. The second 72-hour stoppage will begin two weeks later on Wednesday 3 September.

The walkouts have been deliberately timed to cause maximum disruption to passengers - they will begin at noon on the Wednesday, finishing the same time on the following Saturdays, each causing four days of chaos. In a separate dispute, the union has also ordered 700 staff working for four cleaning contractors employed by LU to strike for 48 hours from 5.30am next Thursday until the same time on the Saturday.

The action is being viewed as a direct snub to Boris Johnson who wants a nostrike-deal for the Tube. On Monday it was revealed that the RMT is engaged in a record seven separate disputes with Tube bosses - which could lead to further strike action.

In its negotiations with Tube Lines, the union has turned down a two-year pay offer of 4.95 per cent for the first year and inflation plus 0.75 per cent for the second year.

Mr Crow said: "Our members on Tube Lines do the same work as colleagues on Metronet and they have today made clear they are not prepared to be left worse off." He argued that Tube Lines made an "enormous profit" from his members' work.

But a Tube Lines spokeswoman suggested there was an "ulterior motive" behind the strikes. She said: "We believe that a pay offer of 4.95 per cent is very competitive, especially when compared with the UK average rise of 3.7 per cent. We are disappointed the RMT is taking this stance and passengers have every right to feel angry.

"The RMT's vote against the offer and the length of their proposed action defy reason and perhaps suggests there is an ulterior motive behind the rejection. They have made no secret of their desire for Tube maintenance to return to public ownership."