Almost 15 million people were left waiting for post over the Christmas period, including 2.5 million who missed important documents, health appointments, or were unable to pay a fine or bills, Citizens Advice research suggests.

More than half of those left waiting (54%) reported going at least a week without letters, while 3% said they could not pay a bill, 8% said they missed an important document, and 7% said they missed a health appointment, rising to 16% of those on an NHS waiting list.

People across London (35%), the South East (32%) and the North West (31%) were most likely to experience a delay in receiving post, the survey of 4,165 UK adults indicates.

Further analysis by the charity suggests the situation failed to sufficiently improve in January, with 23% of those polled reporting disruption to their mail.

Again, more than half of those surveyed (54%) reported receiving no post for more than a week.

Citizens Advice’s monitoring showed disruption peaked in mid-January.

On January 12 and 13, Royal Mail warned that 77 areas across the UK were hit by disruption, affecting up to 2.4 million people in England and Wales each day.

Some of the worst-affected areas, including Chelmsford in Essex, Willesden in north-west London, and Upminster in east London, faced eight weeks of severe disruption.

The charity said the situation appears to have “finally” improved, but noted it is the second year running that it has flagged severe Christmas disruption, with 16.5 million people affected last year.

Citizens Advice is calling on communications watchdog Ofcom to investigate Royal Mail’s performance and consider enforcement action and fines, saying both must learn lessons from the past two years to prevent the same happening again.

Citizens Advice chief executive Dame Clare Moriarty said: “A staggering 2.5 million of us missed important documents, health appointments, or were unable to pay a fine or bills due to post delays over Christmas.

“We understand the strain the pandemic has placed on Royal Mail. But after two years of disruption, Royal Mail cannot let poor service become the new normal. These delays can have serious consequences for those left waiting for their letters.

“Ofcom must now investigate Royal Mail’s performance and consider enforcement action and fines to ensure lessons are learnt.”

A Royal Mail spokesman said: “While the vast majority of mail is delivered safely and on time, the impact of the rise of Omicron had a particular impact during Christmas and January, with approximately 15,000 staff members off work due to sickness and self-isolation at one stage.

“As Citizens Advice has acknowledged, the situation has significantly improved. The number of offices we have reported as being most impacted by service issues has reduced from 77 to just one today.

“We apologise for any delays that our customers may have experienced in the local areas affected. We are working hard to equalise performance and improve service in those areas, including spending over £340 million on overtime, additional temporary staff and sick pay, as well as targeted support.

“Our postmen and women are continuing to work incredibly hard, as they have done throughout the pandemic, and we are thankful for all of their efforts and determination.”

An Ofcom spokesman said: “We know how important a reliable postal service is to customers, and we can take action if Royal Mail fails to meet our annual targets.

“We closely monitor its delivery performance throughout the year, and have made it clear to the company that it must improve as the impacts of the pandemic subside. We will assess Royal Mail’s compliance after it has reported on its overall performance for the whole financial year.”

– Yonder Data Solutions surveyed 4,165 UK adults online between January 14 and 18 to ask them their experience of letter delays between mid-December 2021 and mid-January 2022.