"Martin Edwards" wrote

Remind me: I am from Watford but live in Birmingham. There is a Croxley
and a Croxley Green Station. Which lines are they on?

Croxley is the intermediate station on the Met Watford branch. Watford West
is the (closed) terminus of the LNWR branch from Watford Junction and
Watford High Street. The Croxley Link will be a new link from Croxley to
join the Croxley Green branch, which would be reopened, with teh stub from
Croxley to the Met's Watford terminus being closed. Met trains from Aldgate
and Baker Street via Harrow-on-the-Hill would be diverted over the link to
terminate at Watford Junction.

Peter