Blimey Daicoses, there's a question. It would be hard to describe all the British accents in a few paragraphs and the differences between them but they are very marked.
Just as an example, Geordies (people from Newcastle-upon-Tyne) have an accent that is partly derived from the Vikings. As a soft sooutherner, I find the thick Geordie accent hard to understand but Scandinavians apparently find it easy.
To my ear, the Geordies and the Mackems (people from Sunderland) sound the same but locals will tell them apart. On the other hand, I can recognise a Sussex accent with ease but to my northern friends think that it's just a southern accent.
Similarly, I can tell the difference between, say, a New York or a Georgia accent but would find it hard to distinguish between someone from Georgia and Alabama.
What I find strange about Frasier is that the brother's accent is *so* different from Daphne's. If it were a west Yorkshire or a Lancashire, or a Scouse accent, I could understand it, but the 'Cockney' one just jars. It would be like someone from Brooklyn having a brother who apparently comes from Macon .