As I understand it it started as a 'voluntary' PR effort, then became obligatory unless you could justify it for safety reasons. They were supposed to leave a run of samples for reference, but often did not. Many folks put them back after the war, but many did not.
I have been told of the low grade stuff being dumped in the sea, and in the North of England they were dropped into a quarry site. Urban myth perhaps but it's incredible how the built environment has changed and we assume that stumps sticking out of copes is how our streets should look.......don't get me started etc.....!