The comments follow the deep concern voiced by the union in June at the announcement in the emergency budget that the Government was seeking to divest itself of its interest in NATS.

Prospect’s National Secretary for Aviation, Garry Graham, said: “The great irony is that this means the Bank of America will be advising the UK Government on something that no other country in the world, including the United States, is prepared to do.

“NATS represents a crucial part of the UK aviation infrastructure and is responsible for some of the most congested and complex airspace in the world, so safety and service delivery must remain at the heart of the organisation. "But aviation stakeholders are starting to wake up to the implications of the budget announcement and are increasingly alarmed about the direction of Government policy.

“A sale of the Government’s stake in NATS will lead to instability and a greater emphasis on profit, resulting in a knock-on negative impact on service delivery and safety.”

Not only is the UK unique in the world in having a partially-privatised air traffic control system, it receives no public subsidy and is a net contributor to the Exchequer, said Graham.

“We have yet to hear one single argument from the Government as to why a further sell-off would be in the interests of service delivery, aviation stakeholders or the travelling public.

"This seems to be driven by a combination of the Treasury seeking to fill a hole in Government finances and misplaced ideology.”

Unions representing NATS’ staff will be meeting MPs next Wednesday to raise their concerns.