When did Americans lose their British accent? (2012)
mentalfloss.com
mentalfloss.com
See: https://www.livescience.com/33652-americans-brits-accents.ht...
The real British accent has so much variation, there isn't one. There's a stark difference between my accent and someone's accent just 10 miles away (the Salford and Bolton accents are quite distinct).
Game of Thrones shows a good mix of real British accents if not a bit mishmash (Sean Bean business as usual accent for Ned Stark, plus a Manchester accent from Robb Stark and God knows what from Arya, with a fairly decent mock one for Jon Snow).
https://en.m.wikipedia.org/wiki/Great_Vowel_Shift
Pronunciation in 1600s sounds like a mismash of northern and Scottish accents. The 1600s "mate" is literally how someone from Lancashire would pronounce it. Boat sounds like a mild Scottish accent.