Hi! It's cool that you're aiming for a specific type of accent/pronunciation, but it is really hard to learn an accent unless you live in the area the accent is from. Make sure you use British resources/study materials if you'd like to get used to that accent, but don't force yourself to learn a specific accent as it can sound unnatural/forced.

Yahya, there really isn't a "British" accent in English. There is British English, although all "Englishes" are really not that different in reality, certainly not like Arabic dialects.

I guess you are looking for RP (received pronunciation). Enjoy: https://www.youtube.com/channel/UCz4tgANd4yy8Oe0iXCdSWfA