"Mizter T" wrote

However, given the apparent state of distinct confusion on the matter,
replete with NRES proclaiming that it is valid to use it to Vauxhall,
along with ticket office staff at Vauxhall and seemingly also
Bletchley saying likewise, then if a passenger uses such a ticket for
a journey via the WLL then I can't see how they can possibly be
accused of any wrongdoing whatsoever.

Of course, anyone actually travelling from Watford Junction or north of
there to Vauxhall would be much more likely to go via Euston and the
Victoria Line, and should be ticketed accordingly.

Peter