Mizter T wrote i
..
Just noticed that TfL has launched a new facility on the fares
section
of their website - a "Single fare finder".

http://www.tfl.gov.uk/tfl/fares-tickets/fare-finder/

You input your start and finish station - the fares finder is replete
with a javascript auto-complete function - then select adult or child
and and click on "Show fares".

The applicable fares are then listed - the far cheaper Oyster fares
comes first (both the peak and off peak fares are listed if there's a
difference), followed by the pricey cash/printed ticket fare.

It's basically just a friendly front end to a simple database that
lists which stations are in what zones.

Err, that wouldn't work. The fare finder has to know how many zones
have to be crossed for a reasonable route from A to B and whether this
includes zone 1

I recall it being noted on this NG that some Oyster fares assume a zone
one route is taken. A simple lookup for fares would have 20,000+
entries, making all the contiguous stations on one line in one zone one
entry would chop this down a good deal.

--
Mike D