Surely it is possible to programme any location as a waypoint using either Lat/Long or OS grid refs? Or would that be too time-consuming?
Sure, but indeed time-consuming and error prone. Particularly since you'll want the pencil line on the map to correspond to the magenta line on the GPS, normally. Drawing lines from airfield to airfield is easy.
Well, you could try running the airspace in a similar way to LAX class B and C and providing a consistent, easy to use radar service for all.
Don't forget that LAX, together with basically any major airport in the US, has a 30-nm "mode C veil" ring around it. No mode-C transponder, no access, period. From the recent discussion we had following the mode-S situation in the Netherlands, I don't think the UK is ready for any sort of TMZ. So don't just blame the CAA, NATS or the individual controllers, also blame the mindset of a lot of pilots/owners/operators - see zkdlis post above wrt. Stansted.