Martin Chalk, the general secretary of the British Airline Pilots’ Association (Balpa), confirmed that the aviation industry also feared a shortage of pilots.

One problem was that many have had insufficient time flying commercial planes since the start of the pandemic to keep up with legal requirements and be sufficiently “resilient” to resume their jobs without retraining.

Separately, hundreds are believed to have taken early retirement, with many others switching careers due to a lack of work during the virus crisis. Others have switched to part-time work in what could become a permanent move for many.

Mr Chalk, who was a pilot for 27 years, said: “I have only reached my mid-50s, but I took early retirement last summer because a voluntary redundancy package was being offered.

“There will be other people who have either been furloughed or made redundant and will have gone back to a previous career or picked up a new career – so an unknown number of us will not fly again.

“We have a large number of pilots out of work but, as things speed up and airlines seek to recruit, there is a concern that we might go from a position where we had over-supply of pilots to one where actually sufficient have left the profession that we end up with a shortfall. There is a feeling that, next summer, there may be a shortage of pilots.”

Addressing the number of pilots who will require additional training and flying time before they can transport commercial passengers again, Mr Chalk said: “We are calling on the Government to help airlines re-skill and reinvest in resilience so that particularly next spring, as the work ramps up as we hope it will, there are actually the crew there to fly.”

Balpa is requesting government funding for “resilience training” for pilots grounded during the pandemic, on the basis that airlines’ finances have already been devastated by the pandemic.

Separately, ministers are funding “skills bootcamps” for people seeing to become HGV drivers amid a shortage of trained workers in the haulage industry.

An analysis by consultancy firm Oliver Wyman, drawn up earlier this year, said: “The most important question is not whether a pilot shortage will re-emerge, but when it will occur and how large the gap will be between supply and demand.

“Based on a modest recovery scenario, we believe a global pilot shortage will emerge in certain regions no later than 2023 and most probably before. However, with a more rapid recovery and greater supply shocks, this could be felt as early as late this year.

“Regarding magnitude, in our most likely scenarios, there is a global gap of 34,000 pilots by 2025. This could be as high as 50,000 in the most extreme scenarios. Eventually, the impact of furloughs, retirements, and defections will create very real challenges for even some of the biggest carriers.”