A SERIES of "ghost" planes has appeared on air traffic control computer screens in the latest problem to hit the controllers' new £623m centre.

Garbled radar data has led to some screens at the centre in Swanwick showing non-existent aircraft in the North Sea area.

Now National Air Traffic Services (Nats) has warned controllers of the problem and told them to keep aircraft further apart than normal if the phenomenon occurs.

Nats insisted that the safety of planes was not being compromised.

The problem, highlighted in Computer Weekly magazine, is only one of a number encountered since Swanwick came online in January.

Some controllers have been concerned that they might misread the heights of planes because of difficulty in reading numbers on their screens.

Controllers have said that the latest "ghost" problem did not occur at their centre in West Drayton, west London -- the centre that Swanwick is replacing.

A spokesman said: "The ghosting problem has affected only a few screens and only affects an area of the North Sea.

"Safety has not been compromised, but nevertheless, we felt it right to issue a notice to employees."