Last-ditch talks got underway this morning to try to halt tonight's tube strike as commuters were warned to expect another 48 hours of chaos.
Managers and union officials are meeting at the conciliation service ACAS, but after two days of negotiations an agreement looks increasingly unlikely.
London Underground has published an emergency timetable to allow four million daily tube users to plan their journeys.
The impact of a strike is likely to be even more severe in west London where mainline rail services are being disrupted by floods.
During last week's industrial action, trains into Paddington offered strike-hit tube users an alternative, although many services were overcrowded.
But the Great Western main line is struggling to cope after signal equipment at Maidenhead was flooded.
Some South West Trains are also affected by submerged tracks.
The combination of a strike and the floods could produce a perfect storm for the unions as they ratchet up the pressure on London Underground.
The strike by members of the RMT and TSSA is over plans to close 254 ticket offices with the loss of 950 jobs.