Ok, update.
The rear knock that plagued me for so long was down to a faulty reproduction caliper. I sourced a second hand one from here and it fixed my knocking problem, however it came with its own issue. Whilst painting it silver, I noticed the seals were shot.
So I sourced a reconditioned OEM caliper through 'the brake specialist' on ebay, and used this caliper as a surcharge against the freshly rebuilt caliper.
Great service from the company so far. I've not had my money back for the caliper I sent them yet, but I've no doubt it'll be fine.
Next I was looking it to the hot start issue. The thinking on here is either it's starter motor/voltage related or fuel related.
I opted to start with the fuel. Now, on page one of this thread I said I'd fitted 4 new injectors. What actually happened was I did buy 4 genuine injectors but as it was only one that was faulty at the time, I replace that one with a spare I had knocking around that I knew was good.
Flash forward to today and I swear your honor, I have indeed fitted the four genuine injectors. I'm glad I did as the one injector, the seal looked like this....
and the retaining clip fell apart in my hand
I also fitted a crankshaft sensor. The one on there was a blue plug one, but I found this Febi item for sale on ebay, brand new for £10. Got to be worth a shot?
Old one
New one
*squints to see what's been etched off*
I also fitted a post cat lambda, I had a spare knocking around from past Clios. Brand new bosch item. In an effort to cure the hot start it issue I fitted it. Don't ask me why, I just did.
The car drives amazing now. The idle seems smoother and the car just more eager. Can't explain it.
Hot start issue, seems far improved. But still not 100%. I've checked the starter and it does have its heat shield. I could be being fussy and not appreciating it's a 22 year old.
Anyway, that's it for now...
(old photo wearing its one red caliper)