Well, the water level in the stream dropped a bit today and I managed to re-join the Plass4 connectors and stop the leaks. I cleaned the threads and applied a bit of PTFE tape. Had to tighten them fairly firmly, with a wrench. All I can see written on the black pipe is "POLYPRENE 1972 BS 1" - the writing is nearer white than blue, definitely not green.
John
That would be BS 1972 then another bit on the end.
BS 1972 LD.C (light blue inserts.)
BS 1971 LD.D (light green inserts.)