At least 600,000 passengers cancelled plans to fly from Heathrow in December due to the Omicron coronavirus strain and the introduction of tougher travel restrictions, the airport said.

Fears over the Covid variant meant that, from late November, all travellers arriving in the UK were required to take a pre-departure lateral flow test and self-isolate until they received a negative result from a post-arrival PCR test.

This led to many people scrapping their travel plans over the festive period.

The new rules were relaxed for fully-vaccinated arrivals last week after travel firms said they were ineffective due to Omicron spreading widely within the UK.

A total of 19.4 million people travelled through Heathrow across the whole of last year.

This was less than a quarter of the pre-pandemic level in 2019, and 12.3% down on 2020.

Travel to and from the Asia/Pacific region in 2021 was down 40.3% year-on-year.

The other markets with double-digit reductions were non-EU Europe (down 13.8%) and North America (down 13.6%).

Domestic travel bucked the trend, with a 21.1% boost in passengers compared with 2020.

Heathrow chief executive John Holland-Kaye said: “There are currently travel restrictions, such as testing, on all Heathrow routes.

“The aviation industry will only fully recover when these are all lifted and there is no risk that they will be reimposed at short notice, a situation which is likely to be years away.”

Mr Holland-Kaye warned that this creates “enormous uncertainty” for the Civil Aviation Authority (CAA) as it prepares to set a five-year cap on Heathrow’s passenger charges.

He said: “The regulator must focus on an outcome that improves service, incentivises growth and maintains affordable private financing.”

The CAA increased the cap on Heathrow’s price per passenger from £19.60 to £30.19 from January 1.

Airlines expressed outrage at the decision, claiming the rise was too high.

The CAA is expected to announce a long-term cap running from the summer to 2027 in the coming weeks.