you are british, not nigerian... it doesn't matter what your "roots" are because they are not who you are... YOU are who you are and that is nothing to do with britain or nigeria.
please don't be sad because no one is perfect... i see you as british as do most people... not that it matters...
i understand you are struggling with personal identity but you cannot dwell on what you do not have, and you don't have the nigerian culture or language. if you want to that badly, then take lessons or move to nigeria.
you are worth so much more than the way your dad treats you, none of it it your fault... it is his.. do not believe for one second you are to blame and do not believe it makes you worthless... you are you and you need to be strong. try and be independant, do well in your exams so you can have a bright future free of your parents.