The long-term infrastructure must not be allowed to crumble

Iain Findlay, IPMS

But that was before 11 September, and the subsequent massive downturn in the aviation industry.

Now there are concerns that the owners will be unable to raise the funds necessary to keep the service functioning.

Plans for a �400m air traffic control centre in Prestwick in Scotland have already been put on hold.

Union official Iain Findlay was due to tell the controllers' annual conference on Saturday that such decisions could be disastrous.

"Investment in vital infrastructure... must be maintained according to the original timescale to ensure capacity and safety are not affected," he said.

"The government took the money that has put Nats under financial pressure, exacerbated by the recent tragic events.

"The long-term infrastructure must not be allowed to crumble".

'Strong case needed'

However, it is unlikely that the government - which made �800m from the sale of Nats - would be easily persuaded to hand over any cash.

BBC correspondent Simon Montague said: "Nats would have to make a strong case for more investment, and so far officials won't say if government help is needed.

"What controllers and ministers are doubtless keen to avoid is another crisis of the sort that destroyed Railtrack."

A group of seven airlines - including British Airways, Virgin Atlantic and EasyJet - owns 46% of the company.

The government holds 49%, and employees own the remaining 5%.