Vowels and diphthongs FLEECE, GOOSE

BrC long vowels appear to be only sporadically and lightly affected by the London Diphthong Shift, for UK-born speakers only (e.g. Sally has slightly centralized monophthongs such as  for GOOSE); Jamaican-born ones generally follow both JamC and StJamE in having tense monophthongs. The fully centralized variants of /i:/ [əi] and /u:/  do not seem to co-occur with BrC grammar and lexis, even in code-switching. One wonders whether BrC, like AAVE (Labov 2001), might provide a locus for non-participation in predominant vowel-shifts.