Question about "trap/ash" vowel quality...(British

After listening to some London grime performers,watching few interviews with British R&B musicians, and some indie rock bands (from Brighton), I've noticed that there must be a change in pronunciation of /æ/... Maybe I'm deaf but for me it ranges in quality from /ä ~ a/ - just like my Polish /ä~a/..
So my question is: how widespread is this in the UK?

Crap [kräp] in RP and Canadian English, and by some Californians.
so:
[kräp] is ''crap'' in London and Toronto, but ''crop'' in Phoenix and Miami.