UK == United Kingdom != England.
Geography: The British Isles comprises some 600 or so islands of varying sizes, lying off the coast of northern europe including the isles of scilly, britain, ireland, the inner and outer hebrides, the shetland and orkney islands, plus a lot more.
Politics: There are two sovereign countries within the british isles, the United Kingdom, and Ireland. The united kingdom is split into 4 nations: England, Wales, Scotland, and Northern Ireland. There has been recently some devolvment of power from UK government to individual national assemblies - with varying degrees of success.