The Watford and Edgware Railway (W&ER) was a company established in the 1860s in the United Kingdom to build a railway between Edgware in North London and Watford, Hertfordshire, via Bushey. Its planned 6.25-mile (10.06 km) route would have extended railway line which form part of the present-day Northern line on the London Underground network. Nothing substantial was constructed.
The W&ER had several proposed routes and stations but was generally intended to branch from the now closed Edgware, Highgate and London Railway (EH&LR) just before Edgware station and take a northerly route, with intermediate stations suggested at various times for Stanmore (London Road), Elstree (for Brockley Hill), Caldecott Hill (for Bushey Heath), Old Bushey, and Heathbourne Road. The line was planned to terminate at a station on the eastern side of Watford High Street, close to the site of Watford Central which was later planned by the Metropolitan Railway. One of the alternative proposals had it extend the Watford and Rickmansworth Railway from Rickmansworth in the direction of High Wycombe.
The company's continuing failure to raise the capital needed to construct its line may have been partly due to the competition that it would have offered to existing services. Opposition came from the London and North Western Railway to a junction at Watford and from the Midland Railway to a junction at Mill Hill Broadway. Eventually the Great Northern Railway (purchasers of the EH&LR before its opening) bought out the W&ER and continued to develop proposals although nothing was built.
In 1922 the London Electric Railway (forerunner of most of the London Underground) purchased the W&ER with the intention of using its right of way to continue the extension of the Charing Cross, Euston & Hampstead Railway (CCE&HR, now part of the Northern line) that it was then building north from Golders Green to Edgware. Various plans were made but no construction took place.
Work on the route finally started in 1935 as part of Northern Heights Project through which London Underground was to take over the EH&LR lines (by then part of the London and North Eastern Railway) and join them with 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. Earthworks were underway and the tunnel near Elstree South station and the viaduct for Brockley Hill station had been partly constructed when the start of World War II caused works to cease.
Work did not restart immediately after the war as there were stronger demands on funds for works elsewhere including the reconstruction of many damaged stations and the extensions of the Central line. After the introduction of Metropolitan Green Belt the Elstree and Bushey areas were protected against development, so the need for new stations to serve new residential developments in the area disappeared and the project was cancelled in 1950.