More support for G.
A faster aircraft in the circuit has to space himself according to common sense and the speed of the traffic in front. Very slow traffic in a circuit (which G was by any measure), has a duty to keep it tight, so long as that can be achieved safely.
If you are being overtaken in contravention of the rules of the air on final, then you hold your course. A go around would have been a bad move and would have risked blurring who was wrong and who was right. The only time this goes out of the window is when you need to avoid a collision.
It is very true that over the last few weeks, the vis has been getting gradually worse, and this will contribute to a Microlight becoming almost invisible on final. It is worth sparing a thought for the pilots of much faster machines than PA28s. We find it very hard to spot Microlighters, and it is amazing how often they show up on or close to the instrument approaches near busy airports. It happens more in France than in the UK.
On the Airprox/CHIRP subject, by all means file both. An Airprox clearly occurred, and it will be down to the board to determine whose fault it was and whether a genuine risk of collision occurred. On the basis of your side of the story, the PA28 driver and the FISO risk getting their knuckles slapped - by my reading of the story - There are always 2 sides though.
CHIRP is a great channel to make a wider audience aware of a problem. Yours is not a new problem though, and similar things happen in circuits all over the UK on any sunny day in summer. I guess the questions I would be asking would be:
What specific new learning points would my CHIRP convey that would differentiate it from all the other occasions that somebody gets cut up in a circuit?
If it matters so much, and nobody's livelihood is involved, why does the incident need to be reported secretly?
Just my 2 Euros worth.