That is a constructive answer Easy Street, but there are two aspects of it that I take issue with:
Our good IMC mid-air safety record is largely based on the application of airmanship and UK-only ATSOCAS; it's the pilot's choice whether to get a radar service for IFR in class G and thankfully it seems to have worked over the years.
I don't agree. Collision risk is based on the product of two probabilities:
(A) the probability of an aircraft being on conflicting (i.e. colliding) trajectory with another
x
(B) the probability of the crew not being able to resolve the conflict in time to avoid collision
Generally, pilots vastly overestimate A and underestimate B in perfect VMC.
The human sensory system is not well suited to aircraft collision detection. As a result, the difference between B in VMC and B in IMC, particularly with the help of electronic aids such as TCAS that do not care about flight conditions, is much less than one might naively expect.
As a consequence, collision risk is dominated by A. Which is why for practical purposes all collisions occur in VMC, because the traffic density in VMC tends to be higher than in IMC. In VMC, there is no practical difference between class E airspace and class G airspace at the levels we're discussing.
So what you're doing is encouraging us to spend money and resource on a risk that is theoretical, when we should be spending it on practical measures to avoid collisions in VMC.
No matter how good the safety record in Class G IFR, the fact is that the UK's approach to it is practically unique and non-compliant with ICAO and SERA.
Not so. ICAO and SERA permits IFR in class G, and states like Germany and Switzerland that have previously prohibited it are now trying to work out how to adapt their rules appropriately.
Your comment on ATSOCAS and the "nuances of terrain avoidance responsibility" is a very good one. However, it is not limited to the UK.
Here's an example of a UK pilot in France who presumably thought that an instruction from ATC was terrain-safe. Unambiguous responsibility for terrain avoidance is an important issue, and more attention should be given to it generally. But it doesn't require us to make all airspace controlled. Since Ben Macdui, UK ATSOCAS has been revised to make the division of responsibilities very clear, in phraseology as well as regulation.