"Added to that the company, still reeling from a drop in revenue following September 11, is now being squeezed by the CAA’s economic regulator which is refusing to allow NATS to raise its charges.

"This, in turn, is deterring new external investment and detracting from NATS’ primary focus of ensuring safe reliable air travel."

Following Tuesday’s statement from the Transport Secretary outlining proposals to build new airport runaways, the union says any plans to expand capacity at UK airports must be backed with sufficient investment to ensure the ability of air traffic services to cope with the increased traffic.

"NATS is already facing a financial crisis in that investment promised as part of the privatisation has not materialised, including funding for the new Scottish air traffic control centre," said Luxton.

The union is calling on the CAA to allow NATS to raise its charges and give it the financial headroom to proceed with investment promised as part of the privatization and for future infrastructure.

Prospect represents 3,500 air traffic controllers and engineers in NATS.