--- Angus Bryant said...

"Tom Anderson" wrote

One more thing: the four-tracking on the NLL ends at Camden
Road east junction; the Primrose Hill and Hampstead branches
diverge to the west, at what i assume is called Camden Road
west junction. Thus, you'd need to four-track between the two
junctions; it's not at all far, but it is in a heavily built-up
area.

Is it a genuinely 2-track width, or is there space for another 2
tracks
(i.e. 2 tracks used out of a 4-track-width alignment)?

Two tracks used out of a four track alignment. There should be enough
space to reinstate the missing two tracks. In fact, they should never
have been removed in the first place!