A report from the National Audit Office (NAO) into the delays at His Majesty's Passport Office (HMPO) found they were caused by recruitment challenges, limitations in its systems, and unsuccessful efforts to manage demand - despite efforts to plan ahead.

Due to limitations on digital processing, 134,000 digital applications had to be moved to the less efficient, paper-based system, the report said.

Media reports of delays also created difficulties, it said, as concerned travellers contacted the telephone helpline for reassurance, which placed greater pressure on services and staff.

While 95% of applicants received their passports within 10 weeks, about 360,000 were waiting longer which resulted in travel disruptions for many.

A record 6.9 million applications were processed from January to September this year, an increase of 21% from the same period in the pre-pandemic year of 2019. More than seven million applications were made during the time period, with nearly half received from March to May.

In May alone, HMPO received more than 1.2 million applications, 38% more than the highest month in the previous five years.

Lessons have been learned from the experience, the NAO said. There has been improved contact with customers, capacity is being built to better manage demand in the future and a move to a digital process is being completed, the report read.

Despite that, there was a warning for HMPO as similar demand is expected next year. A further 9.8 million applications could be received in 2023, still higher than average demand.

The NAO urged HMPO to learn the lessons from 2022 so it is better prepared for such demand.

In particular, it was encouraged to focus on improving management of customer expectations, improving management information and working with the Home Office to develop a more flexible approach to managing higher demand.

Responding to the report, a Home Office spokesperson said: "The impact of COVID-19 on passport services is not unique to the UK, with passport issuing authorities across the world having reported challenges for their service.

"We recognise that a small percentage of British passport customers did not receive the service that they should rightfully expect earlier this year. However, we have worked hard to rectify this, and have processed a record number of applications for a British passport in 2022, with over 95% being completed within 10 weeks."