A war of words over strikes raged tonight as commuters faced more travel chaos in the capital because of a walkout by thousands of London Underground workers.
Union leaders took the unusual step of urging the Prime Minister to intervene in the Tube dispute after the latest 24-hour walkout led to huge queues for buses and taxis, costing firms millions.
Leaders of the Rail Maritime and Transport union and the Transport Salaried Staffs Association wrote to David Cameron pressing him to convene urgent talks in a bid to resolve a bitter row over 800 job losses.
The unions said they were taking the "unprecedented" step after accusing London Mayor Boris Johnson of being more interested in using the dispute to shore up his standing among the Tory faithful.
Mr Johnson hit back during a speech to the Conservative party conference in Birmingham, where he launched a blistering attack on the leadership of unions, describing their actions as "nakedly and blatantly political".
Transport for London (TfL) said around 40% of Tube services ran despite the strike, which ends at 7pm today, although the unions claimed there was widespread disruption, with entire lines closed and others badly disrupted.
The letter to the Prime Minister, signed by RMT leader Bob Crow and Gerry Doherty of the TSSA, said: "We hope you would agree that, instead of barracking Tube workers from Birmingham, he should be listening to London and the real concerns of passenger, pensioner and disability groups who are saying the cuts on London Underground will disproportionately hit the more vulnerable in the capital.
"This strike is not about 'irresponsible militants' taking on the coalition; it is about London Underground staff giving up a day's pay to put safety first. Indeed, if the Mayor simply kept to his election promises regarding adequate staffing on London Underground there would be no dispute."
Mr Crow told a news conference that Tube stations would be less safe if the 800 jobs are cut which he said made no sense at a time of heightened concerns about terrorism.
He called on TfL to start with a "blank piece of paper" during any new talks, pledging to suspend two further strikes in November if that happened.
"We hope that today will be the last strike but our members' resolve is stronger than ever."
Mr Doherty added: "We do not intend to strike any deal that compromises safety or leads to a worse service."
The Mayor stepped up his call for changes to employment laws, saying: "It cannot be right that a ballot can lead to strike action when less than half the members of that union take part."
Mr Johnson said at least 50% of union members should take part in a ballot before strikes were allowed but unions pointed out that Mr Johnson was elected on a turnout of less than 50%.
Howard Collins, LU's chief operating officer, said: "We are running more services and serving more of the network than during the last strike. The unions have once again failed to bring London to a halt.
"Although Londoners will doubtless face some disruption, we have 40% of Tube trains running and, together with additional bus and river services, we are keeping London moving."
Mr Crow disputed the 40% figure, saying: "The first casualty of war is always the truth."