91�ȱ�

Passengers on the London Underground (LU) network are enduring disruption to their journeys as thousands of workers stage a fourth 24-hour strike.

Members of the Transport Salaried Staffs Association (TSSA) and the Rail, Maritime and Transport Union (RMT) stopped work at 1830 GMT on Sunday.

The unions say plans to cut ticket office jobs will threaten safety, but LU denies this.

All lines have been affected and are all at least partly suspended.

said 80% of stations were open and 45% of trains were running.

The RMT said the latest strike - the fourth since August - was over LU's refusal to suspend plans for 12 weeks while talks are held.

But Tube management said the unions had not taken up its offer to discuss the cuts proposals further over a six-week period.

The RMT's general secretary Bob Crow said: "The capital is locked down this morning across the board.

"TfL and LU have been reduced to their usual well-rehearsed lies over services that they claim are running but it is pure fantasy and simply misleads Londoners."

He later warned that they were moving towards escalating the action in the new year which could lead to two or three-day strikes.

"I will not be recommending any action this side of 2 January, but come 2011 we will have to consider escalating strikes to more than one day," he said.

But Mike Brown, LU's managing director, described the latest strike as "cynical" adding: "Services are operating on virtually all lines this morning despite the pointless strike.

"We are doing everything we can to get as many Tube services as possible operating, and to keep Londoners on the move with extra buses, river services, and other alternatives."

The following Underground lines are disrupted:

TfL said it had made an extra 100 buses and boat services available and warned of high demand on its cycle hire scheme during the strike.