I had done a reccy of a rather fresh smelling outfall, so returned one evening with Ojay to have a further look.
The from the outfall was a short section of RCP which lead to a manhole chamber, here the pipe turned to brick.
After around 200m was a brick chamber with 2 RCP dropshafts.
A ladder lead up through the ceiling into a stack of concrete chambers that went up around 100ft.
The topmost ladder went to a a narrow shaft that terminated in a manhole, but had a couple of slits. Through these the top of the dropshafts could be seen and a hole into a chamber above which remains unexplored for now.