Jack Taylor:
The H&C line stations were originally part of the GW, with connections to
the West London Railway, together with the crossovers at Paddington allowing
through working (reputedly even a Windsor to Aldgate service at one time!).

The original H&C Railway was a GWR subsidiary at first. It started at
a junction with the GWR at what is now Westbourne Park, and ran south
to Hammersmith, with a branch soon added connecting to the WLR to
reach what is now Kensington (Olympia). It was used from the outset
for through running from the Metropolitan (i.e. the north side of the
Circle) -- initially using GWR tracks between what are now Paddington
(H&C) and Westbourne Park -- and soon became part of the Met for operating
purposes.

Clive Feather:
Even a train to Aldgate that slipped a coach into Paddington main line
station!

Yeah, once.

Incidentally, District trains also ran through onto the GWR to Windsor
for a little while, using a connecting track at Ealing Broadway. This
service operated from 1883 to 1885. The District itself at that time
consisted of two separate pieces connected by the LSWR tracks (now
District and Piccadilly) from Hammersmith to Turnham Green, so these
trains had to change railways three times on each trip.
--
Mark Brader, Toronto | "Whatever you are, be out and out,
| not divided or in doubt." -- Brand (Ibsen)

My text in this article is in the public domain.