British art institution (4)
I believe the answer is:
tate
'british art institution' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tate that I've seen before include "Art gallery founded by sugar magnate" , "Art gallery endowed by a sugar merchant" , "Britain/Modern gallery" , "- - Modern: art gallery" , "Sugar refiner and art gallery founder, d. 1899" .)