This was a great video for me — not being from the Isles, I recognize these myriad dialects but have no idea how the various locales relate to each other geographically.
I realized Yanks talking about places like Michigan, Texas, Maryland, Oregon, Montana, and such, must be like all this talk of Cornwall, Yorkshire, Kent, etc. All I can say is "yup. Those are in England. And Scotland's up there somewhere."
And generally, the best way to 'write accents' is not to do it, but for very sparingly, Emu. More often, it's accepted as better writing to try to convey an accent purely with word choice and ordering. Things like,
"Blimey mate, you really done for him dinne?"
"Aye and where do ye think ye be going?"
"Ay meng, what's this I hear about you messin' with my pushers?
"It is not so much between friends yes? Your friend Nenad tells you this is true."
The general rule is, if your reader has to slow down and figure out what exactly your character is trying to say around the accent they're chewing on, you've done too much accent. And are racist.