The Chiltern system works exceptionally well (as a key user now, who used to be involved in the police aviation world). One a2g talk group across the three forces ( five counties) allows both aircraft to be hailed either in the air or on the ground, and also allows the Oscar ones to negotiate with each other in real time on those rare occasions where there is conflict (the crew have the final call). Also a scramble line to both bases and the three command and control systems in each base allow jobs to be flagged up for review in real time. No national control room required.
I'm not sure why Npas couldn't use a similar regional model, perhaps with six or seven county wide ( not force) hailing talk groups. The borders would need to overlap but the crews and Oscar 1s could manage conflicting taskings. This would take the central control room out of the picture saving both money and time....