Lawrence James or piers brendon both have similarly sized and titled books that both cover up to around the 2000 mark. I bought them for some essays at uni, have yet to read them cover to cover because British history is pretty soul destroying when you look deeply into it. But as far as their style and whatnot, they are both strong books and authors. But you are also better off looking at world history in general owing to the fact that the British empire was very much the reason that Britain is as historical ly significant as it is today. When various world organisations proposed concepts like national sovereignty (which we have even less to this day), then empires and colonies all over the world broke away from each other. You'll struggle to find just one book to summarise it. Perhaps articles would be better, depending on how far you want to take this under the microscope?

Edit: avoid niall Ferguson like the plague. He is a moron just looking to sell books. If you must read his please don't pay him for the privilege.