Royal Mail failed to deliver post on time to an estimated 16 million people over Christmas, research conducted by Citizens Advice found.

The independent watchdog said a “startling” 5.7 million of those had suffered serious consequences as a result, including missing health appointments, fines, benefit decisions and important legal documents.

However, Royal Mail hit back, saying the numbers quoted were not credible and the picture painted did not accurately reflect the tens of millions of customers it delivered to successfully over the festive period.

Citizens Advice said the number of people experiencing postal problems is now at its highest level for five years, aside from 2022 when Royal Mail was involved in strike action.

It found more than a third (36%) who send or receive post sent fewer Christmas cards in 2025 because stamps were too expensive. Another third (34%) reported not getting post for between one and three weeks at a time, then receiving a bunch of five or more letters in one go.

Anne Pardoe, head of policy at Citizens Advice, said: “We’re afraid there’s no light at the end of the tunnel for consumers struggling with Royal Mail’s persistent delivery failures.

“When people have no other postal provider to choose from, the sheer volume of delays is simply unacceptable.

“The company’s dreadful festive slump is about much more than late Christmas cards. People are left distressed after missing health appointments, fines and benefit decisions.

“This is a worrying trend, and with cuts to delivery days looming, Ofcom must start cracking down even harder on missed targets before things go from bad to worse.”

A spokesman for Royal Mail said the numbers relied on by Citizens Advice were based on a sample size of just 2,000 and that Ofcom did not apply normal delivery targets over the Christmas period.

He added that falling letter volumes meant many households no longer received mail every day, which created a perception of delay when post was moving as planned.

The Royal Mail spokesman said: “Independent data shows that more than 99% of items posted by the last recommended dates arrived in time for Christmas.

“This was during our busiest time of year, when volumes more than double, and we’re grateful to our teams across the country who worked incredibly hard to deliver for our customers.”