Royal Mail is losing around 400 postal workers per week, according to the Communication Workers Union, an increase from the 330 per week the company was shedding before it introduced a new delivery system called DM26 earlier this year.

The CWU claims DM26, which reorganises delivery routes and allows second class post to be delivered every other weekday instead of daily, is not working properly in hundreds of offices. The system groups workers into teams of three and changes walking patterns, but staff who spoke to the BBC anonymously report that parcels are still being prioritised over letters, mail is left undelivered, and time is wasted sorting mail by delivery class.

One postal worker in the West Midlands told the BBC: "I didn't take any first class mail out on my last shift because I was on a road that's been behind for weeks. But I'm sure a manager would have ticked a box to say all first class mail went out."

Workers tracked their step counts after the switchover and found increases of between a quarter and a third, often reaching around 25,000 steps daily. Several said they fear this Christmas will be a "nightmare" given increasing parcel volumes.

Bryn Dymott, who delivered post in Bedfordshire for nine years, left Royal Mail in July saying he could not face another "shambolic" Christmas. He said the company is "proving it's impossible to have four people's work done by three people."

The CWU told members to pause further DM26 rollout until problems are addressed. The union says the system is operating successfully in around 500 offices but has run into significant problems in hundreds of others. Martin Walsh of the CWU said: "Put simply, if a boat is already taking on water, adding more passengers is unlikely to solve the problem."

Royal Mail says DM26 is on track for full deployment by Christmas and is delivering to 95 per cent of UK addresses daily, up from 88 per cent before rollout. The company is hiring 22,000 temporary workers for the Christmas period.

The company also announced plans last week to cut 2,500 head office and supporting roles by the end of 2027. Regulator Ofcom has fined Royal Mail more than £37m in three years for missing delivery targets.