Following clearance from the CAA Safety Regulation Group, union representatives have been working with the HSE and management since the beginning of the year to resolve concerns over the clarity of screen displays.

But, on behalf of 3,500 air traffic controllers and engineers at NATS, Prospect has warned of the growing frustration among members that work to rectify operational difficulties has still not been completed.

The HSE conducted an inspection of the air traffic equipment in January after some controllers identified problems with the fonts and ergonomic design at the new centre, resulting in a number of members reporting eyestrain and headaches.

Prospect aviation officer David Luxton said: “While the recent software upgrade at Swanwick is an important step towards correcting the problems, our members are concerned that the remedial work has still not been completed 11 months after the problems were identified.“

The issue is one of a number of subjects - including possible industrial action if any moves to end the final earnings pensions scheme are brought into play - to be discussed at the air traffic controllers’ annual conference taking place at the Bredbury Hall, Stockport this weekend. Speakers include NATS’ chief executive Richard Everitt.