At Heathrow (and other NATS airfields) the UHF frequencies used by tugs and other vehicles which were cross-coupled to the VHF Air and GMC frequencies were dedicated to those tasks alone. By this I mean that ATC and aircraft would only hear calls from vehicles which were of concern to them - runway crossings, towing aircraft, etc. To talk to their bases vehicles switched to another UHF channel which wasn't coupled to any ATC Frequency. ATC had the ability to uncouple the link if the UHF frequency became jammed but I never recall using it. It all worked an absolute treat...
With great respect to my ATCA colleagues I don't like the system outlined by Il Duce. The operation of the manouvring area at an airfield with a licenced ATC Unit should be in the hands of an ATCO. If an incident occurred and the ATCA was at fault, who would bear the responsibility? Probably the ATCO.