About 406,060 international flights operated from the UK this year, compared with 1,399,170 in 2019 before travel was restricted.

UK domestic flights also fell by nearly 60%, said aviation analytics firm Cirium.

Budget airline Ryanair remained the largest carrier in the UK, with more than 100,000 UK flights in 2021.

Rival airline easyJet followed closely behind, with more than 82,000 flights in total, according to data collected by Cirium.

The busiest international route was between London's Heathrow and New York's JFK.

This was despite the US only opening its borders to UK travellers in November.

American travellers have been able to travel to the UK since 28 July.

Short-haul flights proved to be the most popular, with eight out of the 10 most popular routes being to Europe.

London Heathrow to Amsterdam, Paris Charles de Gaulle and Frankfurt came in third, fourth and fifth place respectively.

Meanwhile, the UK's busiest domestic route was between Land's End to St Mary's in the Isles of Scilly.

The 31-mile route saw about 2,330 one-way flights between January and December 2021.

Following a sharp rise in Covid-19 cases throughout the UK due to the Omicron variant, the outlook for 2022 remains uncertain.

The uncertainty has already sparked a rise in cancellations over the festive period because of concerns over potential further restrictions.