The government's controversial part-privatisation of the UK's national air traffic control system has been thrown into question with the revelation that the airline consortium, led by British Airways and Virgin Atlantic, is haggling over the £800 million price tag for the national air traffic service - NATS.

The airline group should have started running NATS on June 1 but a dispute over the price, the airlines estimate it at £600 million, is holding up the deal.