Paul Corfield wrote:

So to test an example - Highbury and Islington should be able to sell a
GNER "Loony Woony Toony" [1] ticket to Newcastle upon Tyne because you
can catch a FCC train at Highbury and then eventually change on a GNER
service at Stevenage or Peterborough?

Or Kentish Town should be able sell you a ticket to Kettering because
you can change from FCC to Midland Mainline at Luton?

I often make medium distance business-related trips with little
notice, and two sensible routes from my office out of London are
Northern Line to Kentish Town and thence by NR, or Victoria Line to
Tottenham Hale or Seven Sisters and thence by NR. I have certainly
wanted to do journeys like your second example -- and had to rebook at
Luton or Bedford.

It does seem to me -- a fairly knowledgeable traveller -- that the
availability is rather random. Tottenham Hale in particular has both
LU and NR ticket offices, but often the NR one is closed and you are
directed to the LU one, which cannot, as you say, issue very many
types of ticket. On the other hand, I discovered recently that Warren
Street tube station can issue a ticket to Stansted Airport.

We often accommodate visitors from continental Europe or the USA. The
former are often used to wholly integrated transport systems and the
latter are unaccustomed to public transport, and both find the London/
UK system rather baffling. In my experience in other places, it is
unusual to be able to buy a ticket from A to B, but not from B to A,
and I think we lead the world in the complexity of our ticketing
options.

I quite agree that you don't want people making lengthy transactions
at a station with a single LU ticket window, but a return to Derby
from Kentish Town doesn't seem to me to be unreasonable, or
necessarily to take much longer to issue than a tube ticket.

Peter CS