London Underground services have been crippled because of a strike by workers in protest at job cuts, causing misery for commuters and other travellers.
All 11 of the capital's Tube lines were hit by the walkout, the latest in a wave of industrial unrest causing increasing concern among business groups and politicians in the capital.
Transport for London said more than 40 per cent of Tube trains were operating, despite the strike by thousands of members of the Rail Maritime and Transport union and the Transport Salaried Staffs Association.
RMT leader Bob Crow said: "All the reports from the front line are that today's action over safe Tube staffing levels is rock solid the length and breadth of the system, as our members send out the clearest possible message to the mayor to call a halt to the cuts before there's a major disaster.
Picket lines were mounted at more than 100 stations and depots, with the unions warning that a fourth strike will go ahead at the end of the month unless the row over jobs is resolved.
The unions are protesting at plans to axe 800 mainly ticket office jobs, although they claim the number is set to rise to almost 2,000.
TfL denied that safety was being compromised and said that by 8am more than 40 per cent of trains were running, compared with 28 per cent at the same time during the last strike, while 50 trains were running on the Northern line, twice as many as last time
TfL launched contingency plans, including more than 100 extra buses, capacity for around 10,000 more journeys on the river, and marshalled taxi ranks.
Around 80 Tube stations will be closed throughout today, including Charing Cross, Westminster, Piccadilly Circus and Knightsbridge in central London as well as Heathrow Terminal 4 in west London.