Well, let me begin by saying that every fellow ought to scratch his fleas as he so chooses. That said, it has always been my understanding that the only way to handle fox is to split the tail so it can dry out okay, then sew it up.
If you are a fur trapper you usually put a raw hide on a wood or wire stretcher to dry as hard as rawhide and sell the fur that way. No salt, that reduces the price you get or the industry may simply not buy your fur. Since we are a pre-1840 community we can consider Canada and the old North West Company (HBC) and the mountain men. Both just dried as stated, no salt.
Big game trophy hunters with caribou, bear, etc. normally can't wait around for a hide to dry so that's when this salt business got started. Salt down the hide and if the salt is too wet- scrape it off and keep using salt until you have got mo0st of the moisture out and then roll the thing up and get to a taxidermist.
The home tanning of hides, there are solutions you can use. I'm not sure how much trapping is done in the UK, maybe the best bet is a taxidermist to either do the job or give advice.