Royal Mail workers tell ITV News Consumer Editor Chris Choi why they're striking
Members of the Communication Workers Union (CWU) expected at least 15,000 to attend the rally, describing it as the biggest postal workers’ demonstration in living memory.
Many among the animated crowd were seen wearing pink hi-vis vests, waving flags and holding placards that read “strike to win” and “save our Royal Mail”.
CWU General Secretary Dave Ward also joined one of the many picket lines, which were mounted outside Royal Mail offices across the country, with little sign the long-running row will be resolved soon.
Strikes are also planned on Sunday, next Wednesday and Thursday.
Andy Mason, a postman of 20 years, told ITV News a time comes when "we need to stand up for ourselves".
"It’s everything from enforced Sunday working, to removal of allowances, it’s the change and the bouncing of the start and finishing times.
"At the moment we start at 6.45am and we finish at about 2.45pm. They wish to change that to whatever they need to, they call it flexible hours."
He added: "To know that there is stuff piling up and being left... and it’s birthday cards, it's Christmas cards, it's legal documents, it's hospital appointments... other customers saying that they’ve missed cancer screening letters.
"That doesn’t sit well. And we will do everything we can, but there comes a point when you have to say 'I’m sorry but we need to stand up for ourselves'."
Andy Mason feels he has to strike, despite the impact he knows it may have on communities
A Royal Mail spokesperson said after three days of discussions they were unable to reach a resolution, saying "all we received was another request for more pay, without the changes needed to fund the pay offer".
They said: "The CWU know full well that in a business losing more than £1 million a day, we need to agree changes to the way we work so that we can fund the pay offer of up to 9% we have already made.
"While the CWU refuses to accept the need for change, it’s our customers and our people who suffer. Strike action has already cost our people £1,200 each.
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"The money allocated to the pay deal risks being eaten away by the costs of further strike action.
"The CWU is striking at our busiest time, deliberately holding Christmas to ransom for our customers, businesses and families across the country.
"We are doing everything we can to deliver Christmas for our customers and settle this dispute. During the last strike days, we delivered more than 700,000 parcels, and more than 11,000 delivery and processing staff returned to work."
The spokesperson added: "We remain willing to talk at any time about our best and final offer and urge the CWU to call off their damaging strike action."
Rishi Sunak suggested he will not meet pay demands
Rishi Sunak appeared to rule out meeting union demands for pay rises for public sector workers to head off strikes before Christmas.
He also declined to provide details of “tough” new anti-strike laws being considered, stressing that he wants to “protect lives and to minimise the disruption” caused by industrial action.
The prime minister was asked whether, aside from asking the military to step in, the government could do anything to prevent the industrial action from going ahead over the festive period.
Speaking to broadcasters at RAF Coningsby in Lincolnshire, he said: “The government is always going to try and act fairly and reasonably.
“What I’m not going to do is ask ordinary families up and down the country to pay an extra £1,000 a year to meet the pay demands of the union bosses. That wouldn’t be right and it wouldn’t be fair.”Chancellor Jeremy Hunt also earlier said the government wants to avoid agreeing to the pay demand of striking workers as it will risk locking in high inflation across the UK economy.