Talks aimed at breaking the deadlock over plans for an all-night Tube service in London are set to resume today.
Rail union leaders will meet London Underground bosses under the chairmanship of Acas, the conciliation service, for a fresh attempt to reach an agreement on pay and conditions.
The night Tube was originally planned to start in September but as negotiations dragged on it has been delayed, with no new date for its launch.
London mayor Boris Johnson cast fresh doubt over the planned service last week when he said it was not "absolutely critical".
The London Underground and Rail, Maritime and Transport are holding last-ditch talks just hours before a three day strike, that could affect millions of people across London and surrounding areas.
Conciliation service Acas said the talks between the RMT and London Underground started at 10am.
RMT union members are set to walk out of their jobs for three days at 9pm this evening, in a long-running dispute with the London Underground over ticket office closures.
A two-day strike last week caused huge disruption, with roads clogged as people switched to other forms of transport.
Old Routemaster buses were in operation around the capital today as Transport for London attempted to keep London moving during the Tube strike.
TfL said there was a record number of buses on the capital's roads after 266 extra buses were brought in for the first day of the 48-hour walkout.
David Cameron described travel disruption caused by the Underground strike in the capital as "unacceptable" on Twitter.
It's unacceptable that millions of people are having their lives disrupted by today's Tube strike in London.
A 48-hour Tube strike has created "total chaos" for Londoners just trying to get to work, one commuter has said.
Emily Toner told ITV London that she was forced to hire a Boris bike because of the crowds at Liverpool Street station:
When arriving at Liverpool Street at the Tube, I discovered the gates were still not open so I resorted to using a Boris bike to get into work.
Total chaos has been caused to good people just trying to get to work.
The RMT union said its members were forced to take industrial action as London Underground "have refused to move one inch" over ticket office closures and claimed the operator had breached an agreement the groups had previously reached through Advisory, Conciliation and Arbitration Service (Acas).
Despite the spin from LU nothing that they are proposing is about 'modernisation'.
The current plans, closing every ticket office and axing nearly a thousand safety-critical jobs, is solely about massive austerity cuts driven centrally by David Cameron and his Government and implemented by Mayor Boris Johnson.
RMT could have recommended the suspension of this strike action if LU had responded positively to our proposal to halt the implementation of these savage cuts, stopping the dire impact they would have the length and breadth of London Underground.
A 48-hour strike by London Underground workers began this morning, causing widespread disruption for commuters in the capital.
Members of the Rail, Maritime and Transport union (RMT) started a 48-hour strike at 9pm last night over a long-running dispute about plans to close Tube ticket offices.
The union says the closure of ticket offices will cost hundreds of job losses and threaten safety, while LU says staff would be better employed on station concourses as only 3% of tickets are bought at ticket offices.
Normal underground services will resume tomorrow night at 9pm before a a three-day stoppage from 9pm next Monday.
Boris Johnson has hit out at senior members of the RMT union over the 48-hour strike on London Underground.
The Mayor of London said the strike was only happening because some "union barons" were trying to "flex their muscles" in a bid to succeed former leader Bob Crow, who died in March.
Despite dozens of meetings over several months the RMT chose only on Friday to make fresh demands. It seems they are more interested in fighting over the leadership of the RMT than the interests of their members.
Commuters and businesses will suffer because a few narrow minded union barons are currently flexing their muscles in a fight for the leadership of a union where just 30% of members support a strike.
Women who have been pictured eating on the underground and their images uploaded to a Facebook page have been urged to contact the British Transport Police, the Evening Standard reports.
Facebook page 'Women Who Eat on Tubes' is encouraging the public to upload pictures of women eating on the underground, which has caused a stir on social media.
Captions of what underground line they were on and what they were eating is also displayed.
The page states in its summary: "Subjects are embraced and cherished. We celebrate and encourage women eating food on tubes, we do not marginalise them. WWEOT is observational not judgmental. It doesn't intimidate nor bully."
Speaking to the Evening Standard, Director of Enforcement and On-Street Operations Steve Burton has advised passengers:
"If any customer has concerns about such behaviour, believing there may be a sinister motive, they are advised to speak to our staff or the British Transport Police."
Please dial 0800 40 50 40 or text 61016 if you need to contact the British Transport Police