We need to know why they can't bring this system on stream, on time

Gavin Strang MP

But in order to do that the system must work perfectly by this December to allow a year to train air traffic controllers.

Labour MP and former Transport Minister Gain Strang said the Swanwick system was "hugely important".

Speaking on the BBC's Today programme, he said: "If it is not going to be working on time then we have to find out why, we cannot just go on and on like this.

"We need transparency, we need to know why they can't bring this system on stream, on time."

Good progress

The number of bugs in the system is falling - 400 technicians have brought the number down from 500 faults in recent weeks.

And Bill Semple, Chief Executive of Air Traffic Control, said he was confident the system would be ready.

There will be no compromises made as far as safety is concerned

Bill Semple Chief Executive, Air Traffic Control

"There is still a lot to do but the fact that we are down to this number of so-called bugs now is extremely good news for us."

He said good progress had been made since an independent audit last year found around 1400 bugs in the system.

"Now we are down to 200, we have a very comprehensive plan for fixing them and we are confident that we will have this system ready for operation in December.

"There will be no compromises made as far as safety is concerned, and if there are any doubts on that account I can assure you that I will not take this system into operation," he added.

Swanwick uses one of the world's most complex computer systems.

The Hampshire centre was due to open in 1996 at a cost of about �350m.

But costs have spiralled and the centre is now at almost twice its original cost at �623m.

Safety fears

The delays to its opening have prompted fears about the ability of the current centre at West Drayton to cope with the amount of aircraft flying into and out of the UK.

But National Air Traffic Services always maintained that West Drayton could safely handle flights for some time and that safety was not being compromised.

Managers at Swanwick have admitted that there is a medium-to-low risk that all the computer problems will not all be solved in time.

But Tony Collins of Computer Weekly magazine warned that risk could increase "if any of the bugs turn out to be more difficult to fix than they had originally thought".

"This is a piece of software with two million lines of code," he added. "They have had enormous success in the last few months, it is just a question of whether they can keep that up."