The firm said the downturn, which started in October and has since been exacerbated by Omicron, was comparable with the one observed following the emergence of the Delta variant back in March.

ForwardKeys said there had been "relatively steady growth" in air travel this year, rising from less than 20% of 2019 levels in Q1 to more than 50% come Q4 and peaking at 64% in the last week of October.

However, it said the year had been punctuated by two setbacks, the first coming in the week beginning 12 March when the week-on-week growth in bookings was reversed from +11% to -10%, coinciding with the worldwide spread of Delta.

The second started in the last week of October, with bookings continuing to slow since then. By late-November, they were down to 54% of 2019 levels, "correlating closely with a fresh rise in Covid-19 cases since late October".

"It is now likely the emergence of the new Omicron variant, and the travel restrictions introduced in response, will inhibit demand for last-minute travel over the Christmas period," said ForwardKeys on Tuesday (7 December).

Olivier Ponti, ForwardKeys vice-president of insights, said: “2021 has definitely been a year of travel recovery; but that recovery has been bumpy and patchy, with many established destinations displaced and several tourism-dependent destinations making valiant efforts to retain the patronage of leisure travellers.

"It has also been a tug of war between a strong pent-up demand to travel on the one hand and travel restrictions, imposed by governments to inhibit to the spread of Covid-19 on the other.”