Air travel across the globe has slumped during the coronavirus pandemic – but Heathrow airport could use the virus to justify more flights in future, anti-expansion campaigners have warned.

Flights to the west London airport have collapsed as countries shut their borders in response to Covid-19.

Passenger numbers were down 90 per cent last month – with just 700,000 people travelling through Heathrow in April, averaging around 45 planes a day.

Flights to Heathrow normally land on one runway, and take off from the other – but with fewer planes, the airport switched to using just one landing strip in early April.

It is rotating which runway is used each week, giving residents a break from flight noise.

But campaigners warn that Heathrow has proposed similar measures in the past as a way to expand flight numbers.

When the airport is running at full capacity this “mixed mode” operation would allow an extra 80,000 flights each year, according to environmental group Airport Watch.

Heathrow abandoned plans for intensive runway use in 2013 – more recently it has proposed a third runway, with Government giving the green light in 2018.

The vote split the Conservative party – with then Foreign Secretary Boris Johnson, whose Uxbridge constituency is near the airport – opposing the plans, but not attending the vote in Parliament.

As Mayor of London, Mr Johnson had previously said he would “lie down in front of those bulldozers” rather than see the airport grow.

A recent Court of Appeal ruling said the current plans are unlawful, because they would stop the UK meeting climate change targets.

Heathrow is appealing to Britain’s top judges in the Supreme Court – but campaigners warn that intensive use of existing runways could be an alternative way to expand.

Stop Heathrow Expansion’s Geraldine Nicholson said residents must not be “lulled into a false sense of security” by the drop off in flights during the pandemic.

Quieter skies have been a “welcome relief” for locals used to the “constant barrage of aircraft overhead”, she said.

But though the Court of Appeal ruling against the third runway “dealt a significant blow” to the airport’s expansion plans, the “relentless pursuit” of growth will continue, she claimed.

“Some may think that mixed mode would be the lesser of two evils and a solution to Heathrow’s expansion problem,” she said.

“The reality is mixed mode would bring an end to the current half day respite from aircraft noise, increase ground noise, increase road traffic, reduce air quality and of course increase emissions impacting climate change.”

No 3rd Runway Coalition policy director Paul Beckford said the change was a “concern” for locals.

“Because the Third Runway is looking increasingly unlikely to go ahead – or at least it will have a delay – the airport may move towards mixed mode for expansion,” he said.

“That then has an impact in terms of loss of respite for communities around the airport.”

Mr Beckford said using mixed mode during the pandemic would not strengthen the argument for a longer term shift, as its “not comparing like for like”.

Heathrow cannot increase flights beyond the current 480,000 annual cap without planning permission – and local council Hillingdon opposes any growth.

But the airport could appeal to the Government for support, Mr Beckford said.

And any option to expand the airport without building the controversial new runway could be popular with by ministers, he warned.

“I think if Heathrow had mixed mode expansion it could be politically attractive to a Prime Minister who has opposed the Third Runway,” he said.

Heathrow chief executive John Holland-Kayes has said he is “not even thinking about the Third Runway” during the coronavirus pandemic.

“I am confident that the UK will need it at some point in the future – whether that’s ten years time or fifteen years time,” he said in a recent BBC interview.

Mr Holland-Kayes said the pandemic is the “biggest crisis that we have ever seen in aviation”.

Heathrow Airport was approached for comment.

The Government has since March 23 ordered everyone to stay at home unless absolutely necessary to fight the spread of coronavirus. You can find the latest guidance here. Advice on the virus from Public Health England is available here.