what details about visas etc do i need to know about and where can i get them?

Since Hong Kong grants a 180-day free entry for UK passport holders, you only need to apply a single-entry L type for mainland China. You can apply it the CVASC branch in London, Edinburgh, or Manchester. Just choose the center which has jurisdiction over your residence. Prepare the following documents: your valid passport with at least six months' validity and two blank pages, an filled application form affixed with your recently-taken color photo, a declaration downloaded from the website of CVASC ang signed with your signature, roundtrip air tickets and hotel booking records.