I used to by from Elpees (I think) in North Heath. There was also a shop in Erith if you were desperate.
Then I started buying in the West End. Steve's Sounds off the Charing Cross Road was good for a while and there were a couple of good shops in Berwick Street, plus two or three more in a back street behind the junction of Oxford Street and Tottenham Court Road. Places to get the clear vinyl 7" of Vienna by Ultravox, or the picture disc OMD 12" of Locomotion.
My mum, Ivy, worked in Elpees which was handy going to Erith comp, Lunchtimes spent listening through their secondhand albums.