HMT's power
I respectfully suggest that whilst NATS power over RAF is low, HMT's power is more or less total.
Currently, HMT decides what flying gizmos the RAF can have, and when. For instance, do the RAF actually want replacements, for, say, Pumas? Of course they do. Who decided how many new jet toys RAF would get? Not the MoD!!
If Northolt gets in the way of R3, HMT will decide.
It might not be an issue if NATS/CAA figure out how to Safely use Northolt and R3, but if they can't, then HMT will win. My (1975) wall-covering OS map of the area suggests to me that it will be difficult.
Thanks for all your replies, I'd better get off your site now!