Go with Bristol Ground School -
www.bristol.gs if
They are brilliant: Prepare you so well and you can buy their databank of questions which is invaluable for subjects like law!
Oxford not so good in my view - their books are nice but really expensive and contain more information on some subjects than is required. Not necessarily a bad thing but for distance learning, without someone there to talk you through it can make it harder to learn and you will be revising stuff you don't particularly need. The bristol notes are written really well and with the exam questions in mind so definitely give you the best chance.