So if it's really busy and you're controlling a string of arrivals you don't even bother telling the pilot about the unidentified return in your 12 o'clock
Yeah, but when you've gotten to that point, the controller must prioritize. This is where IFR<-->IFR separation is the priority.
It is hoped the guy flying VFR would have
seen and avoided the other traffic by this point which reduces that risk.
Even VFR Flight Following can be terminated when the controller is too busy handling IFR traffic.
So even if it looks like there's a conflict, you wait for the pilot to request avoiding action
Nah. The finer detail is in the text -it doesn't read 'If and ONLY if' a pilot requests avoiding action.
How would you tell that from a primary-only contact which doesn't have to be speaking to anyone?
Just vector the guys you know who are talking to you around the guys who aren't.
On top of that I'd wager that if you asked professional pilots inbound to Glasgow what class of airspace they flew through and what the rules were for it, half of them would be amazed to hear it could have unknown non-radio non-transponding VFR traffic in it, flying just below the cloudbase in vis as low as 1500 metres.
It's ain't uncommon to have non-tradio non-transponding traffic in the same environment, but what is weird is to allow flight
just below the cloudbase in vis as low as 1500m.
Class E in the US dictates VFR must always be satisfied if you're not IFR (or SVFR) - therefore there is a rule to maintain 500 feet below, and 1000 feet above cloud. If you can't maintain VFR, just talk to ATC.
So if Glasgow is reclassifying E to D, it sounds like the zone is getting busier.