Well, most of us here use commercially produced juice from the grocery store, or fresh pressed juice from a local orchard. There are a few here who press their own apples, but even fewer still use actual cider apple varieties. As you're in the UK, I'd think you'd have better luck finding real cider apples than most of us in the USA. It might be worth the effort if you're already planning on pressing your own apples. Here's a link you might find useful: http://homepage.ntlworld.com/scrumpy/cider/homepage.htm
Click on the recipes, they list some cider apple varieties & the ratios to use. Click on the UK cider makers list & give some of them a phone call, maybe they'll sell you some of their cider apple juice to ferment at home, same goes for any local (or not so local) orchards. If not, regular old store-bought "mystery" apple juice will do, just so long as it has NO PRESERVATIVES. A lot of juices have added ascorbic acid (vitamin C) and that's OK to use. Hope this info helps. Regards, GF.