Post Office workers are to stage a five-day strike in a continuing dispute over jobs, pensions, and branch closures.

The Communication Workers Union (CWU) said the walkout would start on Monday 19 December and include Christmas Eve.

Thousands of staff are expected to take part from Crown Post Offices – the larger brances that are usually located in High Streets.

The last day for first-class Christmas post had been 21 December.

But shop counter staff will walk out on 19, 20 December and Christmas Eve, while cash handlers are preparing to strike on 22 and 23 December, which could cause severe disruption to the service.

Union bosses have said the strike will slow deliveries in the run-up to the holiday.

Andrew Furey, assistant general secretary of the CWU, said: “It will be absolute chaos in the lead-up to Christmas because it’s prime time for deliveries. The main impact will be on parcels and packages.”

In April 2016, the Post Office announced plans to transfer up to 61 branches into WH Smith stores over the following year.

It said the move was part of a 10-year plan to cut costs and save cash, and would act as a way of “safeguarding the future of the network”.

But many staff object to the scheme, which has put up to 400 jobs at risk.

“Our members want the Post Office management to pause its closure and privatisation programme, hold off on its planned pensions changes, and commit to sitting down with us and with the other key stakeholders of this Great British institution and, together, construct a lasting vision,” Mr Furey said.

Kevin Gilliland, the Post Office's network and sales director, claimed it would be “business as usual” despite strike action as 50,000 Post Offices would still be available at its busiest time of the year.

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But he said he was still very unhappy with the decision taken by staff and the union.

“We are extremely disappointed that they prefer to resort to calls for strike action and we will be reviewing our position in light of this development," he said.

Mr Furey suggested the union had been left with no choice but to respond to an “unprecedented attack on jobs, job security, and pensions”.