John B wrote:

...and then on from Mill Hill East to Edgware.

Reviving the Northern Heights plan has been floating around London
officials and geeks alike for years. It would be more sensible for the
Northern Line than serving Mill Hill in the current way, which causes
delays and provides a fairly crap service (and was only built to serve
the barracks at Mill Hill during WWII...)

I thought when Mill Hill East was opened the Northern Heights plan was still
officially an option, albeit on hold, and Mill Hill East was just seen as
bringing forward part of the plan because of the war.