Quick chance to support British (5)
I believe the answer is:
brisk
'quick' is the definition.
(I've seen this before)
'chance to support british' is the wordplay.
'chance' becomes 'risk' (synonyms).
'to support' says to put letters next to each other (in a down clue, some letters hold others up).
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'risk' after 'b' is 'BRISK'.
(Other definitions for brisk that I've seen before include "Spry" , "Bustling" , "Quick and invigorating" , "Lively, invigorating" , "Quick, active, energetic" .)