In article , Ronnie Clark
writes
Presumably, the four tracks heading towards Rickmansworth pair off to two
tracks after Moor Park

Not quite. The Watford branch turns off the slow pair, then the two
pairs continue together for a little further before merging into one.
Exact distances are on my web site.

This pairing by direction does not appear to continue north of Harrow,
judging by the track-plans I have. It merely separated the GC and Met lines.

No: north of Harrow all four tracks belong[ed] to the Met. The GC just
ran over the fast (or the slow when things were broken).

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