PhilD wrote:

The 4th rail goes as far (more or less) as Kilburn High Road. LU has
emergency access rights over this stretch, but I'm led to believe that
the 4th rail isn't in situ for the whole stretch. I am also led to
believe that a battery electric loco sometimes runs to/from Kilburn
High Road some nights.

Don't know about now, but the 4th rail was definitely continuous a few
years ago (during the partial closure of the North London Line)
because I remember being surprised by a Bakerloo line train at KHR. It
sat around for quite a while, then went back the way it had come. I
can't remember which track(s) it used.

It must have been that time, because I have never needed to go to
Kilburn High Road at any other time.

Colin McKenzie