Talks with unions have been inconclusive and have now moved into a statutory 45-day consultation period.

A Heathrow spokesperson said: “Discussions with our unions have taken place over four months and our final offer is informed by feedback we have received from them. 

“But with air travel showing little sign of recovery, these discussions cannot go on indefinitely and we must act now to prevent our situation from worsening. We have now started a period of formal consultation with our unions on our offer, which still guarantees a job at the airport for anyone who wishes to stay with our business.”

Heathrow’s offer will mean pay cuts, changes to benefits and reduced pensions for workers who choose to stay in their jobs.

The spokesperson said: "In order to create consistency across our colleague grades,  the proposal we have put forward to unions aligns salaries to the market rate and addresses legacy contract issues which is currently seeing some colleagues paid some £10,000 more than others doing the exact same job.

"Over half of colleagues’ salaries will either not be affected by these changes, or will be better off.  Of those impacted by the changes, most will see a salary decrease of 15% to 20%. No one’s salary will fall below the London Living Wage.

"For the those whose salaries affected, we are offering a number of choices to help them transition to this new salary, including a lump-sum payment of allowances and salary difference for two years, a phased reduction of salary over three years and for those worst affected in their salaries, we are also offering to re-open up our voluntary severance scheme for the small amount of colleagues whose salaries are impacted by 15% or more."

The airport said the pandemic had cost it more than £1 billion since the start of March.

“Provisional traffic figures for August show passenger numbers remain 82% down on last year and we must urgently adapt to this new reality,” it said.