London museum (4)
I believe the answer is:
tate
'london museum' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tate that I've seen before include "Sugar merchant and art gallery philanthropist, founder, d. 1899" , "Either of two galleries in London" , "Lord Sugar" , "Sugar refiner and art gallery founder, d. 1899" , "Britain/Modern gallery" .)