My recollection is walking up those stairs and right at the top there, just inside the door on the left, would be a stool with a doorman perched on it.....the mum would always be loitering nearby and as you say, would keep a beady eye on who came in.
The Market Diner was nearby-ish, a flat...
I spent many a night in there in the mid to late 80s. I think my night of choice was Saturday. You could set your watch to the times certain songs would be played :lolol: