Important:
ACCENT REFERENCES: This guy is funny and since most of us know our IPA, he has great generalities that he teaches with letter/vowel specific suggestions for putting on a cockney accent. https://www.youtube.com/watch?v=1WvIwkL8oLc
Same guy, but with a take on “posh” high class British accents… including a special guest to give you the difference between modern and more archaic accents. https://www.youtube.com/watch?v=Nj0Rh__1kDw