These rather innocuous concrete blocks,were placed here in 1940 as an integral part of the London Defensive Ring, as a tank trap.The line,mostly still intact,follows the eastern edge of the London Underground Central Line, between Newbury Park station and Barkingside station.
see http://en.wikipedia.org/wiki/Outer_London_Defence_Ring
see http://en.wikipedia.org/wiki/British_hardened_field_defences_of_World_War_II