さっきリンクした発音教室のサイトでは、GB (General British) という概念を採用してますね。

https://pronunciationstudio.com/gb-english/

"Although the terms are hotly debated by academics, the reality for learners is that the name used for the accent model is not really significant. The subtle differences between RP and GB will only concern the most advanced of students; most will simply choose between an American or British model, to this end it makes sense to use the terms General American and General British." 現実的! 「学習者がざっくり理解するには便利な概念。細かいこと言うのは学者」