There seems to be no end in sight to the bitter postal dispute after union leaders announced a fresh wave of strikes for next week.
The Communication Workers Union (CWU) served notice of a third wave of national walk-outs next Friday, November 6 and Monday November 9.
Meanwhile, about 77,000 delivery and collection staff are due to walk out across the country during Saturday, the last of three days of stoppages this week.
Mediators said both sides would this weekend be considering a series of proposals designed to end the "high pressure dispute," which is over jobs, pay and modernisation.
If no breakthrough is found, up to 120,000 CWU members will walk out from 3am on both days next week causing more huge disruption to mail deliveries, the union said.
Earlier, TUC general secretary Brendan Barber, who has chaired the talks between Royal Mail managers and the CWU, said more work was needed to "finalise the terms of a possible settlement".
He told reporters it was a "difficult and complex dispute".
"Despite all the pressures of the dispute, both the CWU and the Royal Mail thought it would be right to come in again today to explore if we can resume substantive negotiations to build on the progress that was made earlier this week," Mr Barber said.
He said both sides would consider "a number of proposals" over the weekend and consult with colleagues "with a view to returning to the TUC for further negotiations early next week".
Royal Mail has estimated there are 35 million items of mail delayed by this week's strikes. A spokeswoman could not give an estimate of how long the backlog would take to clear.