Support for British expert (5)
I believe the answer is:
brace
'support' is the definition.
(I know that brace is a more specific form of the action support)
'british expert' is the wordplay.
'british' becomes 'br' (abbreviation for British).
'expert' becomes 'ace' (ace can informally mean very good).
'br'+'ace'='BRACE'
'for' is the link.
(Other definitions for brace that I've seen before include "Pair - supporting beam" , "Two of a kind" , "Tighten, strengthen" , "prepare for impact" , "A pair as of game birds" .)