Royal Mail workers will stage a fresh strike on Sunday in the long running dispute over pay, jobs and conditions.

Members of the Communication Workers Union (CWU) are embroiled in an increasingly bitter row which has sparked a serious of walkouts.

More strikes are due to be held in the run-up to Christmas, which the union said will cause a huge backlog of mail.

Thousands of CWU members joined a huge rally in central London on Friday to show their ongoing support for the strikes.

CWU general secretary Dave Ward said: “Royal Mail bosses are risking a Christmas meltdown because of their stubborn refusal to treat their employees with respect.

“Postal workers want to get on with serving the communities they belong to, delivering Christmas gifts and tackling the backlog from recent weeks.

“But they know their value, and they will not meekly accept the casualisation of their jobs, the destruction of their conditions and the impoverishment of their families.

“This can be resolved if Royal Mail begin treating their workers with respect, and meet with the union to resolve this dispute.”

A Royal Mail spokesperson 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. 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. We recovered our service quickly, but the task becomes more challenging as Christmas nears.

“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.”