Now,just curiosities beside a railway,these concrete blocks were placed here during the dark days of 1940,when German Invasion was considered to be imminent.These blocks ran from Newbury Park Station,along the eastern side of the London Underground's Central Line,up to Barkingside Station.They represented a tank trap,as part of the London Defensive Ring.
see http://en.wikipedia.org/wiki/Outer_London_Defence_Ring
see http://en.wikipedia.org/wiki/British_hardened_field_defences_of_World_War_II