Alpkit down?
Although down may not be the best choice in the damp British climate.
Sigh, the usual misconception from somebody who probably doesn’t use down for anything other than going to the paper shop, i have used down sleeping bags and down vests in numerous mountain marathons in very wet conditions, perfectly fine, keep it as dry as possible and it will be no problem at all.
I’ve used down sleeping bags for years, and currently the only other thing I have is a down gilet – I always keep them in dry bags in my bike panniers, and, as you say, no problem at all, but you do need to be careful with them.