Hi.
Well, it's a year on since starting this thread and I never did come across the 'perfect' jacket, so I have finally settled for the following, which does not meet all my requirements and I have had to make a few modifications/additions to it already and am planning on making more to get it closer to what I wanted.
https://www.amazon.co.uk/Malamute-Heavyweight-Waterproof-Detachable-Deatchable/dp/B00IOO5MXY [nofollow]The main problem with this jacket is that the hood suffers from almost the exact same problem as described in my first post regarding the Mountain Warehouse jacket, i.e. short zip attaching hood to jacket, leaving gaps for air to get in and hood not deep enough, leaving side of face and ears to become cold; one of the main parts of the body that I needed to be covered, like in my old cheap jacket. There was a comment in this thread that my requirement of having a longer zip that attached the hood sounded like a wind up, however, after having actually now experienced wearing a jacket with a hood attached by a short zip, I can say that the long zip is 100% definitely one of my main requirements in any future jacket I buy!
On the plus side, it is thicker than any of the several jackets that I bought and returned and definitely warm in the body/sleeve area. If only the hood/hood attachment was designed better! Also, the main zip works well, without any fabric or flaps getting caught. I have only been out in very light rain so I cannot comment on the waterproofness yet but it the main body area/sleeves do seem to block wind quite well. The two side pockets are just about high enough to keep my hands in and not way too low.
Just thought I'd update you all. Thanks for all the helpful advice; all of it was very much appreciated!