The union boss whose members brought much of the London Underground to a standstill last week has held out hope of securing a deal to avert another Tube strike.
However, Eddie Dempsey, general secretary of the RMT, warned of more walkouts if a compromise could not be reached with Transport for London.
Peace talks are due to resume on Wednesday in the wake of five days of rolling action that led to a near total shutdown of the Tube from Sunday evening until Friday morning - the first strike to close the Underground for two years.
Mr Dempsey told BBC London radio on Monday morning: "I am hopeful, I'm almost optimistic but I've seen a few negotiations go wrong. I think we'll make some progress in these discussions."
The dispute is primarily centred on the RMT’s wish to move towards a 32-hour, four-day working week for Tube staff to address longstanding concerns about fatigue linked to early and late shift patterns.
TfL data seen by The Standard shows that as many as 650,000 journeys a day were made via Tube stations – though many of these were passengers passing through the ticket barriers on their way to and from the Elizabeth line, which remained open.
All 16,500 Tube staff have been offered a 3.4 per cent pay rise. In a BBC TV interview, recorded last Friday and broadcast on Sunday by the BBC Politics London programme, Mr Dempsey indicated that the pay offer was acceptable.
“We're not looking for more money on top of the 3.4 per cent,” he said.
TfL’s chief negotiator Nick Dent invited the RMT to the peace talks last Thursday, saying: “We want to discuss the issue of fatigue management with you and would like to continue this dialogue next week.”
Mr Dempsey, who has demanded a summit with London mayor Sir Sadiq Khan, told BBC London radio: "I think it would be remarkably foolish if we get the cold shoulder at the first meeting from TfL.
"We'll take our time with it, we'll do the best we can to come to a reasonable settlement, we'll consult our people and if we can get ourselves into a position where there's a compromise that works on both sides then we'll settle.
"We don't want to come back out into strike action but if this all collapses and we turn up for the talks and get the cold shoulder and there's no progress, no movements, I'll have to go back to my members and ask them what they want to do next and the answer is probably more strike action."
He added: "Londoners can rest assured: you only see us when we're on strike but the majority of things we do is settle deals.
"We're a union that makes deals everywhere and we've settled hundreds of pay claims this year and this just happens to be one where we've hit the buffers."
RMT members voted in favour of going on strike to try to win a slight reduction in their working week – something that TfL has said is unaffordable and impractical.
The strike ballot was carried out in July and is valid for six months. However the RMT would have to give two weeks’ notice of any further strikes – and no new dates have been announced yet.
Only 57 per cent RMT members took part in the vote – while about 4,200 members did not participate.
RMT members across all grades – including station staff, drivers and signallers - took part in the strike, with different groups walking out at different times to maximise the disruption.
But a majority of drivers did report for duty, as more than half belong to Aslef – though some Aslef members refused to cross the RMT picket lines.
This means the Tube should be open as normal on Sunday, when Oxford Street will be closed to traffic for the day to showcase Sir Sadiq’s wider vision of pedestrianising the street.
In his earlier interview with BBC Politics London, Mr Dempsey said RMT members were prepared to strike again if TfL doesn’t "make serious progress" on "fatigue and shift work”.
He said: "We're always prepared to negotiate, and we're always prepared to strike."
But he added: “Look, Londoners can rest assured we will go to the negotiating table and we will make every effort to find a reasonable solution to this dispute.
“And if we can't, our members will have to come through their democratic structures and decide what steps we take next.”
