On Thu, 9 Jun 2016 09:46:26 +0100, Clive Page wrote:

What I wonder is how do they work it out for journeys which one can do
in any of three ways (TfL only, NR only, and both) where there is only a
common gate-line at each end, for example Farringdon to Kentish Town?

In that case it doesn't matter, it is an "interavailable" route and
each operator's tickets are valid on the other (this applies between
West Hampstead and London Bridge or Elephant).

In all cases, the Oyster/contactless fare is whatever it says on:
https://tfl.gov.uk/fares-and-payment...le-fare-finder

....which is £2.90 peak, £2.40 off-peak. The TfL cash fare is £4.90
and it seems from brfares.com that the NR cash fare is £3.30.

Richard.