 Work on the route finally started in 1935 as part of Northern Heights plan, through which London Underground was to take over the EH&LR lines, then part of the London and North Eastern Railway, and join them to the Northern line.This extension adopted much of the W&ER's concept, including the location of the junction between Edgware and Mill Hill, the location of the station at Edgware, and the route from Edgware to Old Bushey.The planned extension was to terminate at Bushey Heath due to funding limitations, but provision was made in the design of the station for a further extension to Old Bushey.