Flight below 500ft could be done according to the rule: not closer than 500ft to any structure,vessel or person(something like that!),so pretty much anywhere If you are brave,you could in theory fly down an estuary away from bridges and boats at 5ft amsl.Not much time if you have an engine faliure though!
As for ramblers,they have to get the reg first and since they will probably be too busy shouting at someone like me on a mountain bike they probably wont notice!
I have done pfl's down to about 20ft agl taking advantage of the rules,after all if you don't go down to the ground you never know if you would make it.(watch out for the cables)
No complaints about me being irresponsible please
