Steve,
Stay away from fishing manufacturers, they are well over priced.
Use the layering system, this will allow you to be alot more comfortable, it's not good buying a really thick warm and waterproof jacket, as you will have to wear that same heavy jacket all the time.
It would be alot better to get a WINDPROOF warm jacket and separate waterproof jacket to put over the top.
Windproof is important, as no mater how thick and warm the jacket looks (in the shop there will be no wind), once you get out and exposed to the elements, you will know it's a bad purchase. The hiking type shops are good, however you can get exactly the same jacket from somewhere like screwfix as you can that had Rab, Northface on it for alot less, another company to look at is Keela (scottish company) not well known and quality of clothing is excellent.
Outer layer, get yourself some Army goretex, if you want to splash out a bit more and look different to the others, the the US ECWCS is better as this is 2 layer instead of the British 1 layer.
Enjoy the shopping.
I only have one fishing related jacket, one of the trakker ones that is the puffa jacket, very warm.