On Tue, 2 Oct 2012 15:07:03 +0100, "Tim Roll-Pickering"
wrote:

Charles Ellson wrote:

In fact is there a clear list anywhere of which pairs of stations
definitely
are and aren't valid through interchanges on a single ticket?

For Oyster :-
http://www.whatdotheyknow.com/reques...on_interchange

There are also "emergency OSIs" mentioned in :-
http://www.oyster-rail.org.uk/out-of...terchange-osi/
(PVAL = passenger validator)

Thanks. I assume the regular ones are also valid for paper tickets?

I suspect some of the permanent OSIs might be found in assorted
historic ticket inspectors' instructions. IIRC Kilburn High
Road/Kilburn Park and Kenton/Northwick Park (and the now West
Hampsteads?) feature in a 1938 LMS book.

I'm surprised that Aldgate & Aldgate East aren't a regular OSI - the number
of times that a Hammersmith & City train is nowhere to be seen would make
that a sensible route.