theres loads down the lanes, always on the tarmac when i was a kid they always nested in the pisswhips at the sewerage works, great big blue brick circles full of gravel, 4 arms on wires that were driven around by a 2 stroke fantic engine, the piss went out the arms and was filtered through the gravel then it was pumped into the grass plots around 40 acres of wetland graded and filtered through water cress, they nested in the centre where there was a bearing and 4 segments, sometimes there was 4 nests in each bearing one for each arm segment. these bearings were floated on mercury, fook knows