Thanks for the info'.I'm amazed at the site of the Greenford track,I know it well as one of my son's plays football there regularly.I can only assume that the houses that surround it now were not there then although there probably weren't many Nimbys around in those days.There is also a small enclosed non-league football ground adjacent to the main A40 on what must have been the site. As for Elstree, as you are unsure of the location I wonder if it could have been at the junction of what is now the A41 and A5183 opposite the old L.T. Aldenham bus overhaul works ( remember Summer Holiday, Cliff and his mates) ,about 40 years ago there was a flapping track there which consisted of a straight 200 yards or so dog race track.On the other hand it could have been contained in the Elstree Aerodrome site as I seem to remember reading in a V.S.M.article about Roger Frogley being connected with the flying club there. Any other theories anyone?