Ah, the old UHMRA.
Once, in a Jodel.
'Upper Heyford G-ABCD'
Errr G-CD squawk 7040'
'Negative transponder G-CD'
'Errrr G-CD you're not painting'
'That's 'cos we're made of wood...
Fast forward 30 years to last week, in an OGAR touring Motor Glider, class 'G' airspace. Same thing, no transponder, no primary return, but this time controller very helpful with a basic service, just asked us politely if we could avoid his instrument approach 'feather' while he had an airliner inbound. No problem at all for us, he was very happy with our occasional position reports as we went sniffing for lift. (Gained 800' in 3 mins with the engine off, very pleased with that as a beginner to soaring).
Personally, I'd MUCH rather comply with:
a) if transponder equipped, obtain basic service so that the controller can separate deconfliction traffic from me
b) if not so equipped, maintain a reasonable distance from the instrument approach path so that he doesn't have to send airliners miles out of their way. The very LAST thing we want is the nonsense that has occurred elsewhere with similar traffic density of Class 'D' or some ghastly mess of a radio mandatory or transponder mandatory zone which won't improve safety but just make lives more difficult. Our local ATC unit don't want that any more than we do.
TOO