Northern line extension to Mill Hill scrapped in 1954 left three lost stations
Brockley Hill, Elstree South and Bushey Heath were planned but never built after post-war green belt laws halted the scheme
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Residents of Mill Hill and Edgware today travel on a Northern line branch that could have been three stations longer. A 1930s Transport for London (TfL) scheme proposed extending the line beyond Mill Hill East to Brockley Hill, Elstree South and Bushey Heath, with the latter intended as the new terminus. The project was cancelled in 1954 after post-war planning laws made the stations unviable.
The extension, known as the Northern Heights line, would have linked the Northern line’s two branches, creating a continuous route northwest of Edgware. At the time, a Great Northern Railway line already ran beyond Mill Hill East, but the TfL plan aimed to integrate it into the Underground network. Construction began, with tunnels dug beyond Edgware station and a viaduct built for Brockley Hill station.
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Why the extension was abandoned
The Second World War interrupted work on the extension. After the war, the government introduced green belt legislation to restrict urban sprawl. These laws prevented large-scale housing development around the proposed stations, leaving TfL with no passenger base to justify the project. In 1954, the scheme was formally scrapped.
Most of the infrastructure was dismantled, but parts of Brockley Hill station remain. The viaduct, intended to support an elevated platform, is still visible near the A41 Watford Way. A lay-by for a bus stop, built to connect passengers to the station, also survives. The tunnel beyond Edgware station was sealed after the project’s cancellation.
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What the extension would have meant for Mill Hill
Had the extension been completed, Mill Hill and Edgware would have gained faster connections to central London. Brockley Hill station would have served the area now covered by the A41 and the Royal National Orthopaedic Hospital. Elstree South and Bushey Heath would have extended the line into Hertfordshire, potentially spurring new housing and commercial growth.
Today, the nearest Tube station to the lost sites is Edgware, which remains the northwestern terminus of the Northern line. Commuters from Mill Hill rely on the Thameslink service or buses to reach central London. The abandoned extension is a reminder of how post-war planning reshaped London’s transport network.
No plans to revive the scheme
TfL has not announced any plans to revisit the Northern Heights extension. The green belt protections that halted the original project remain in place, and no new housing developments have been approved near the proposed station sites. The remnants of Brockley Hill station are now part of the local landscape, with no formal protection or plans for preservation.
Questions this report answers
+Why was the Northern line extension to Mill Hill cancelled?
The extension was scrapped in 1954 due to post-war green belt laws, which blocked residential development near the proposed stations. Without enough passengers, the project became unviable. The Second World War had already delayed construction, and the new planning rules made completion impossible.
+Where can you still see remains of the lost stations?
Parts of Brockley Hill station are still visible. The viaduct, built to support an elevated platform, remains near the A41 Watford Way in Mill Hill. An abandoned bus stop lay-by, intended to connect passengers to the station, also survives. The tunnel beyond Edgware station was sealed after the project was cancelled.
+How would the extension have changed travel in Mill Hill?
The extension would have added three stations beyond Mill Hill East, improving connections to central London. Brockley Hill would have served the area near the Royal National Orthopaedic Hospital. Elstree South and Bushey Heath would have extended the line into Hertfordshire, potentially boosting local development.
+Are there any plans to revive the Northern line extension?
Transport for London has not announced any plans to revive the scheme. The green belt protections that halted the original project remain in place, and no new housing developments have been approved near the proposed sites. The abandoned infrastructure is not currently under consideration for reuse.
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