Tom Anderson wrote:

The other end of the pipe is not Cricklewood: it can easily be
followed to Fortis Green Pumping Station in Woodside Avenue N10.

Perhaps arguable; i think that's a different pipe which also connects
to Cricklewood. Although that's really a matter of semantics.

Not really: it was either built as one project or two. Since the pipe is
practically a straight line[1] from Fortis Green to the Hoover Building
forecourt, and the Cricklewood pumping station is a little off to one side,
it is a single pipe.

We should do a map of all underground features in London that are
identifiable from the air.

There already is one - it's called Google Earth ;-)

[1] It goes a bit mental around Woodheyes Rd and Mulgrave Rd. It's almost as
if they had already built most of the alignment from Hanworth to Forts Green
before their plan to demolish some houses in this area was scrapped.