In message , Barry Salter
writes
I would've thought a fairly good place to start would be the list of
stations that are valid for cross-London transfer for National Rail
ticketing purposes, as that'll give a vague idea.

That's a surprisingly long list.

Does anyone know: if you have a national rail ticket coded for
cross-London travel will it work at any of these, or just the two
(typically) that are adjacent to the appropriate national rail termini?
E.g. if you are going from say Cambridge to Bristol, but upon arriving
at King's Cross you decide to avoid the over-crowded tube station by
walking to Euston Square, will the ticket work there? And if so is it
technically valid to do this?

--
Clive Page