In message , at 23:09:13 on Tue, 10 Sep
2019, Basil Jet remarked:

The Milestone Hotel in Kensington has a "1.5 Miles to London" milestone
outside it. This seems to be the distance to Hyde Park Corner.

That's in the mould of the early AA distances - to a gateway on the edge
of London.

It is definitely *not* the distance to CHX, St Pauls or Westminster.

The Sainsburys in North Finchley has a milestone with "8 miles to
London" outside it. This seems to be the distance to either CHX or St
Pauls,

Holborn Bar, perhaps.

but probably not Westminster

Westminster (or Big Ben) is a red herring.

or Hyde Park Corner.

Hang on, the answers are here. There are lots of different origins.
http://www.metadyne.co.uk/n-milestones.html

Lots of different routes, doing their own thing. But the only distance
which had to be standardised (cf "Railway time") was for postage.
--
Roland Perry