77 Parliament hill is just a short walk from Booklover's Corner, up a sharp hill and on the edge of a park. Orwell moved here in February 1935 after living over Booklover's Corner. He had the first floor (American second floor) room in the back. He only stayed until August moving to 50 Lawford Road, according to Orwell's London.
A plaque over the front door commemorates Orwell's stay. I don't know if the mortar discoloration behind it is a result of installing the plaque or caused by condensation from the window sill above. It is impossible to tell from the photo in Orwell's London whether the plaque was there in 1984, so I don't know how old it is.