Artist sitting on bank on very few occasions (6)
I believe the answer is:
rarely
'on very few occasions' is the definition.
'artist sitting on bank' is the wordplay.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'sitting on' means one lot of letters go next to another.
'bank' becomes 'rely' (I've seen this before).
'ra'+'rely'='RARELY'
(Other definitions for rarely that I've seen before include "Seldom, not frequently" , "once in a blue moon" , "when hundred-to-one horse wins?" , "Not very often, seldom in fact" , "very well" .)