Man framing Burlington House member’s “Sea creature” (7)
I believe the answer is:
grampus
'sea creature' is the definition.
(grampus can mean a killer whale)
'man framing burlington house member's' is the wordplay.
'man' becomes 'gus' ().
'framing' means one lot of letters goes inside another (inserted letters are framed by the outside letters).
'burlington house' becomes 'RA' (venue for Royal Academy art exhibitions).
'member' becomes 'MP' (Member of Parliament).
'ra'+'mp'='ramp'
'gus' going around 'ramp' is 'GRAMPUS'.
(Other definitions for grampus that I've seen before include "One often spouting" , "Popular name for a killer whale" , "Killler-whale" , "Marine mammal (heavy breather)" , "Killer-whale" .)