Tim Roll-Pickering wrote

How would you solve the other problem of people with season ticket
travelcards starting journeys outside London? e.g. if I go to stay
the night
in Surrey, I cannot get an overnight return extension - I have to buy
the
ticket on the day.

no overnight return (unless you are 35+ miles out perhaps)

but

http://www.nationalrail.co.uk/times_...asing_tickets/

You can buy Anytime and Off-Peak tickets up to a year in advance,
however you'll only be able to buy these over the telephone or at a
station ticket office.
==

So you can buy a BZ6 extension for today and a single for tomorrow

(a) before you start

or (b) the "ticket for tomorrow"after arrival if the ticket office is
open
or (c) from the arrival station's ticket machine as a "ticket for
tomorrow" after 15:00


--
Mike D