Heathrow has announced that its cumulative losses from the Covid-19 pandemic have hit £2.9 billion.
Fewer than four million passengers travelled through the west London airport in the first half of the year.
It took just 18 days to reach that total in 2019.
The airport warned that its passenger numbers could be lower this year than in 2020.
Some 22.1 million passengers used the airport in 2020, with more than half of those travelling in January and February, before the virus crisis led to a collapse in demand.
Heathrow described recent changes to the quarantine and testing requirements for people arriving in the UK as “encouraging”, but warned that the rules are “holding back the UK’s economic recovery”.
The airport’s chief executive, John Holland-Kaye, said: “The UK is emerging from the worst effects of the health pandemic, but is falling behind its EU rivals in international trade by being slow to remove restrictions.
“Replacing PCR tests with lateral flow tests and opening up to EU and US vaccinated travellers at the end of July will start to get Britain’s economic recovery off the ground.”
In an interview on Times Radio, he asked: “Where is the vaccine dividend?”
The Department for Transport has committed to holding a formal review of the traffic light system “no later” than Saturday.
Heathrow’s revenue dropped from £712 million in the first six months of 2020 to £348 million in the opening half of this year.
Meanwhile, pre-tax loss widened 18% to a little over £1 billion.