Just 19.4 million people travelled through the west London airport last year.
That was down 12.3 per cent on the previous 12 months, and represents the lowest annual total since 1972.
The airport blamed its poor performance in comparison with European rivals on the UK’s tighter restrictions on international travel.
Quarantine hotels remained in operation in the UK for several months after they were scrapped in most other European nations, putting many people off travelling abroad.
Later in 2021, the UK was the only country in Europe requiring both a pre-departure test and post-arrival test for all arrivals, regardless of vaccination status.
European hub airports which recorded a year-on-year increase in passengers in 2021 include Frankfurt (up 32.2 per cent), Amsterdam’s Schiphol (up 22.0 per cent) and Paris Charles de Gaulle (up 17.7 per cent).
Cost savings of £870 million were achieved by Heathrow in the past two years, but pre-tax losses still came in at £3.8 billion due to high fixed costs and low passenger numbers.
Bosses said they are hopeful for a strong summer rebound, contributing to 45.5 million passengers using the airport this year, but they reported lower-than-expected passenger numbers in January and February.
Chief executive John Holland-Kaye described 2021 as “the worst year in Heathrow’s history”.
But he said demand is “starting to recover” and the airport is working with airlines to “scale up our operations”.
Terminal 4 will be reopened for the peak summer season when passenger numbers are expected to increase.
Mr Holland-Kaye added: “We’re excited to welcome more passengers back to Heathrow to experience the joys of travel and get Britain’s economy firing on all cylinders again.”
