I think it is good to be proud of what you are and where you come from, though like most of us, I have mixed ancestry, from Scandinavian invaders to Russian Jewish refugees from the pogroms. My husband, sons, father-in-law and many others all served in the armed forces and none did anything to be ashamed of, as far as I know. FiL was killed in the DDay aftermath, and some uncles were killed in that war too: the war that had to happen to remove Hitler and the Nazis.
But mainly, I think the best part of being British is that our complex hybrid language is the world language. True, more people in the world speak a Chinese language than English, but English is so very widespread, and is the lingua franca of most of the world.
Furthermore, our law is the basis of law in so many countries, and is from a great base: not retributive justice, not religious 'justice', but habeas corpus and cold rule of law. I'm especially proud that Britain and much of the commonwealth have abolished the death penalty.