I attended a seminar by Bernard Porter ("The Lion's Share", "The Absent-Minded Imperialists") today and thoroughly enjoyed it. He's as entertaining as his writing. My favourite quote from the evening:

"The British approached empire like a young man who gets his girlfriend pregnant. They wanted that things which cause empire, but when empire came along as a result, they didn't want to take responsibility for it!"

Read his books, including the new one which comes out next month ("Empire and Superempire"). I guarantee that you will be entertained.