Do nothing to support British fire (5)
I believe the answer is:
blaze
'fire' is the definition.
(I know that blaze is a type of fire)
'do nothing to support british' is the wordplay.
'do nothing' becomes 'laze' (laze around).
'to support' is a charade indicator (letters next to each other) (in a down clue, some letters hold others up).
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'laze' put after 'b' is 'BLAZE'.
(Other definitions for blaze that I've seen before include "Sensationally announce" , "glare" , "Burn brightly" , "Inferno" , "Fierce fire" .)