Hi Coresend
Alan is right, it was behind Cavendish School, when I lived in the area as a child there where flats there called Havelock Gardens.
On an old map there is a sort of triangle created where Upper Beckwith St and Brassey St meet, Havelock St would have been one of the streets in there.
On the modern google map there is a place called "wired" which identifies where the school used to be, if you put the "google man" into Brassey St behind "wired" this is the general area.