Supporter of British artist (3)
I believe the answer is:
bra
'supporter' is the definition.
(a bra gives support to breasts)
'british artist' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'b'+'ra'='BRA'
'of' acts as a link.
(Other definitions for bra that I've seen before include "I give a couple a lift" , "Chest supporter" , "Underwear item" , "support" , "one carrying chest" .)