Royal Mail has blamed stormy weather and too many workers being off sick after complaints over missed delivery rounds and late letters.

The strain on the postal service has meant rounds are missed on a daily basis and letters have been left undelivered for weeks, according to the BBC, which cited reports from more than a dozen Royal Mail postal staff at different delivery offices.

Royal Mail said “short-term disruption to certain routes” was due to “adverse weather, including storms Goretti, Ingrid and Chandra in January, alongside higher than usual sick absence”.

“Where a delay affects a route, we work to resolve it as quickly as possible by putting in extra support and reviewing performance daily to restore deliveries as quickly as possible,” they said.

The company said that, while it aimed to deliver letters and parcels on time, parcels accounted for more of its deliveries and took up more space in depots and vans than letters.

Royal Mail workers also claimed parcel deliveries were being prioritised over letters, which the company has previously denied. The company has said large volumes of parcels can pile up quickly and create a health risk at depots.

The delays come almost a year after the £3.6bn takeover of Royal Mail’s parent company, International Distribution Services (IDS), by the Czech billionaire Daniel Křetínský.

While the Communication Workers Union (CWU) said it favoured the takeover over sticking with its former board as the deal was being finalised, it has since expressed frustration with the new owner.

Craig Anderson, a CWU regional official, told the BBC that Royal Mail was “a company in crisis”.

“I’m not confident that the service is going to improve going forward, it certainly hasn’t since Christmas,” he said.

There is growing frustration with Royal Mail’s service. The consumer watchdog Citizens Advice found it failed to deliver letters and cards on time to about 16 million people over the Christmas period.

However, IDS told investors this month that Royal Mail had delivered 99% of overall items on time in the final three months of last year. Its revenue in that period rose by 1.6% compared with the same time last year to £2.4bn.

It delivered 424m parcels, up 8%, but the number of addressed letters dropped 9% to 1.5bn, even with the Christmas card boom.

In July, the regulator Ofcom gave IDS permission to end second-class post on Saturdays and reduce the service to alternating weekdays from Monday to Friday. The cost of a first-class stamp has more than doubled since 2020, to £1.70, while a second-class stamp costs 87p.

But in October, the regulator fined Royal Mail £21m for missing its annual delivery targets. It was the third time the 509-year-old postal service was fined by the watchdog, and the third-biggest financial penalty Ofcom has issued to any company.

The CWU was approached for comment.