I recall in the late 1970s, maybe early 1980s, a single line, not electrified, off the East London line, south of Surrey Docks (now Quays), swinging round on a curve, going under the lines from London Bridge, and heading off towards New Cross Gate. It didn't look as if it was used much, and I don't know if it still had a connection at New Cross Gate (I was looking down from some tall flats in Reculver Road).
The trackbed has been built on now, although the line that came off the ELL at the same point towards Peckham Rye, lifted during the First World War, has been reinstated for the Overground route round to Clapham Junction.
Does anyone know i) why the line towards New Cross Gate was kept until the 1980s; ii) how the trackbed round to the South London Line managed to be kept clear, not built on, for a century after the track was lifted?