"Charles Ellson" wrote

Which "earlier days" ? Before the 1960s there was only one pair of
tracks from Harrow to Moor Park and BR trains did not stop at
intermediate stations.

April 1960 ABC shows that BR trains served all the intermediate stations
between Harrow on the Hill and Moor Park. Several called at Pinner and
Northwood, but the other stations were served occasionally. There even seems
to have been a through train from Chesham to Marylebone.

The Watford branch was only opened in, IIRC, 1926, and was electrified from
the start. For a few months it was served, about equally, by Metropolitan
electric trains from Baker Street and LNER steam trains from Maylebone.

Peter