In message

, at 02:00:09 on Wed, 5 Mar 2014, Recliner
remarked:
Same thing at KXSP between Thameslink and LU, yes?

Yes (in reference to just one fare being charged).

True, though I don't know why people would change there rather than at
Farringdon, apart from the lack of step-free access at the latter.

It would be a bit out of the way to go from Luton to (say) Victoria, via Farringdon.

Yes, as you may have guessed, I was thinking if the sub-surface lines.

If you were heading east on the subsurface lines anyway, changing at
Farringdon is better (than Kings Cross). Although the paired-by-use
layout ensures the maximum amount of star-climbing is required. [Perhaps
they have lifts too, after the rebuild].

There's a small fly in the ointment though. If someone has arrived on a
"London terminals" ticket, that's not valid to Farringdon, and I presume
therefore it's not strictly allowed to travel to Farringdon and then
touch-in on Oyster from there. (And vice versa on the way home).
--
Roland Perry