I get all my leather tools and leather from mainly one place down towards holloway, it stocks mainly only veg tanned leather, high quality skins, it has some of the modern gold and silver skins which some are obviously chrome tanned but more for fancy looking hand bags and what not, his pig skins, rabbits, goat and cow are all very good.
Also handy I find for small projects are two metre sq boxes of scraps, also the leather thong maker they sell works very well, but you need to have lots of fresh blades handy if you want to get really thin thongs like I use.
The other place I use for small veg tanned suedes and some leather is portabello market, if you come out of the tube, cross the road, and go through the alley way, he's about half way down, not very reliable when it comes to ordering supplies for you, but he has offered me a full size cow hide rug for 50 quid before, and it was nearly 20 ft sq. I use his suedes for making shoulder bags. and pouches and other soft stuff.
Thats if your near or can get to london easily.