It would be nice for me if all of the Airport Operators employed their own staff and then competitive pay levels could take-off.
They aren't stupid. . ..
By shouting " Monopoly" they hope to get a cheaper deal while NATS bears the loss.
Meanwhile NATS continues to "subsidise" them by accepting contract terms that are less than ideal , by tightly integrating Terminal Area and Approach sectors and by providing a stream of rejected trainees - who , given more time , train up into useful airfield controllers.
It's a free market out there unless you're involved in NATS Enroute.