An investigation has started after two jets nearly collided when equipment failed at a new �623m air traffic control centre.

The pilots of the Boeing 777 and 737 passenger jets could not be warned they were on a collision course, last Monday, because of the failure.

A trainee controller at the Swanwick centre in Hampshire accidentally put the two Heathrow-bound British Airways planes on course to potentially hit each other.

However, when his instructor pressed an override button, which would have allowed him to warn the pilots, the device did not work.

Although this can be classed as a near miss, the two planes were two miles apart horizontally

Aviation expert

The trainee did manage to warn the Boeing 777 pilot to stay above the Boeing 737, but the two aircraft passed close enough to each other for the incident to become an official near miss.

The incident is being investigated by the Joint Airprox (air proximity) Board.

An aviation industry source said: "There was a system problem - no doubt about that. But there was no real risk of collision.

"Although this can be classed as a near miss, the two planes were two miles apart horizontally."

The Swanwick centre was due to open in 1996, but constant computer software problems meant it did not become operational until January 2002.

Financial downturn

Since then, there have been computer problems at both Swanwick and another air traffic control centre, at West Drayton, west London.

Although not the same as those on Monday, the problems have led to controller-pilot communication difficulties, resulting in many flight cancellations and delays.

National Air Traffic Services (Nats) was privatised, amid much opposition, last year.

Since then, the downturn in air traffic after the 11 September terrorist attacks has led to Nats facing severe financial problems.