A computer software problem at the UK's main air traffic control centre in Hampshire has caused flight delays at all UK airports.

BBC News Online talks to David Learmount, operations and safety editor of Flight International magazine, about what happened and the implications of the problem.

What has happened?

The National Air Traffic Services, in the middle of the night, uploaded some new software to upgrade their capability. That's a sort of ongoing process - it happens on quite a frequent basis. The upload this time apparently went perfectly well when it was done during the night when there are very few working positions and air traffic controllers on duty because there are very few aeroplanes in the sky.

When it came time for the new shift - the morning shift - to clock on in time for the morning rush hour which starts at about between 6am and 7am, some of the work stations simply wouldn't fire up.

The system basically had been made to crash, only they didn't know about it until the rush hour started. What happened as a result of that was that they had night-time capacity for dealing with daytime traffic. This causes delay and cancellation to a lot of flights.

They literally refused take-off permission to a lot of aeroplanes all over the world bound for the UK, knowing that the UK would not be able to take them.

How embarrassing is this for the industry?

This is really embarrassing. Since the new system has come online, there have been a couple of computer failures. They were computers, however, which were the old ones at the old air traffic control centre, but the information from them was still used by Swanwick.

This is the first time that they've had a major collapse of the system at the new air traffic control centre.

Did they know it was going to happen at some point?

They didn't know what was going to come up. Whether it's with a new model of car or something else, the nature of them is that if you knew there was going to be a problem you'd fix it before it happened.

Teething troubles are things you don't know are going to happen.

Does this have implications for air safety?

It does have implications for being able to go where you want to go. But safety, no - they just don't muck about with safety.

Is it going to happen again and will it be worse?

I don't think anybody knows the answer to that. All we do know is that the system has good backup and standby systems so that safety won't be compromised whatever does happen.

Who is to blame for this?

I suppose you could blame the authorities, and here we're going right back to the time before the system was part-privatised - right back to the time when this new system was conceived.

Basically we could have stuck with the old system. It just would have been flooded and then aeroplanes would have been delayed anyway, because the old system had a finite capacity.

This system is the world's most sophisticated. If you want to blame anything, I think maybe you've got to blame an ambition to be the best, to go ahead of the crowd and to risk using new software.

How long is this system expected to last?

The new system is a new computer with massively more capacity than it needs to have. The old one was a computer - or at least was backed by a computer - which was working flat out all the time.

This system should be able to cope at least for another 20 years. However, it's being upgraded, just like the old one was, all the time - at least the software is being upgraded all the time. This happens every few months - it was an attempt to upgrade the software that caused the system to crash.