I would have thought most of the older roads in SE23 were built with a combined sewer - after all, before cars, the run off from the roads would effectively be sewage. And so no home built before 1920 will have a separate connection for the gutters.

Since then sure, they probably have added low capacity sewers (if the PV pools and gutter streams are anything to go by) to channel the road run off. Maybe some newer homes have connections to that. Where this oily run-off ends up is another question - the River Pool?

Anyway, I was imagining you could walk through these local sewers - this 18 inch sewer in PV is a massive disappointment to me.