I don't think there is such a thing as the accent varies dramatically across the British Isles. For example, the Doric from around Aberdeen is unlikely to be understood by someone with a Gordie or broad Liverpool accent. The BBC used to use something called received pronunciation which was considered to be a bland and neutral british accent but genuine regional accents are more favoured now. Ref:
What am i suppose to say? Hey there this is Sara and i'm from Germany. I have moved to London and people make fun of my accent. I want to get a British accent so that i don't have to be ashamed of my accent.