Sitka over any of the Euro gear... be aware though, sitka gear made for cold weather is made for Alaska cold, not Yorkshire cold! lol... I have a friend who is a sitka sponsored guide in New Hampshire.. I can connect the two of you if you like, he can get any of the Sitka gear with discounts..
Or, has been said already, Kuiu which is a better choice for UK weather (better colours too.. the sitka gear tends to be much more snow and wood oriented rather than conifers and greens, i.e. temperate zones) The better suited sitka ground camo is only available from Sitka Russia apparently!
he's sponsored by Kuiu too! lol
My only concern with Kuiu is that it's main USP is ultra light weight... its seriously amazing gear but I don't think it would necessarily stand up to rough shooting or wildfowling, it is a lightweight layering system rather than a rough and tough jacket.. sitka is slightly more heavy weight.. Have a chat with James if you get in touch, he's a brit in the states and will be able to guide you with knowledge of the gear and our climate.