Garry Graham, National Secretary for Aviation, stated: “This is exactly the type of instability we warned of at the time of privatisation.

"When NATS was sold to the Airline Group we were given a commitment that it was in it for the next thirty years – and had no exit strategy. They also committed to running NATS on the basis of ‘not for commercial gain’.

“Despite these commitments, and in a year when the Airline Group have received record dividends from NATS, it is clear that some want to cut and run.

“Our members have served the airline industry and the travelling public well. We have one of the best safety records in the world despite our airspace being some of the most congested and complex, and delays are at an historic low. Our members feel betrayed.”

Prospect has asked the government to step in. “We said at the time and still maintain that air traffic control is too important to be left to the vagaries and instabilities of the market. The government is now discovering why no other country in the world has gone down the route of privatisation.

“Air traffic control is of such strategic and national importance that the government needs to step in and provide the stability and certainty such a key public service demands.”