Not William Walton although she does seem to have had connections with Walton. This is another composer... (trying not to be too generous with the clues.)
PS. Be fun to see you at the meetup on Thur - see gwl discussion thread.

Sorry, Bill, I seem to have overlooked replying to this. Yes, it is the statue of Mozart in Orange Square just of Ebury Street.
I'm still not entirely clear what the connection with E. Sitwell is but I think Edith Sitwell might have written a book about Mozart?