The latest problem affects the Workstation Display Manager (WDM) software. This system is responsible for drawing radar displays and presenting information to flight controllers.
Contractors who were recently laid off from the project claim the system is showing "cracks" and may miss its much revised launch date in January.
One of the sacked contractors told CW360.com:"In the latest tests, as the radar moves, it drags bits of the screen with it so the background goes blurry. After an hour you can't see anything at all," said the contractor, who asked not to be named.
NATS has battled with several political and technical problems in the past and has been forced to push the system's launch date back several times since the early 1990s. The agency denies this latest revelation is a problem and insists the system will go live on January 27, 2002 as planned.
"I'm happy to tell you that Swanwick remains on schedule and that NATS and the Civil Aviation Authority, its regulators, are satisfied with the radar screens," NATS spokesperson Richard Wright told CW360.com. "There are no problems with the aircraft blips picking up the background, so it's all on track."
The system being developed is years behind schedule and millions of pounds over-budget. The project has been riddled with software problems, and at one point was reported to have "thousands of bugs".