peter wrote

Further out, on some buses the driver always asks my destination and
issues me with a zero charge ticket, while on others it's enough to
wave the pass at the driver. Is this because some local authorities
pay by journey, while others have a bulk settlement?

They all pay by journey but it's a matter for the bus company and the
local authority how that's done and this may depend on the type of
ticket machine in use. A small number have suitable electronic readers
for ITSO cards.

Thus a TfL driver will press a appropriate button when a (non-Freedom)
bus pass is waved, in the same way as when a paper ODTC is shown.

In Surrey I have observed both press buttons (Abellio) and zero charge
tickets (Countryliner). I found GUIDELINES FOR OPERATORS pdf on Surrey
CC's web site which may be of interest.

http://www.surreycc.gov.uk/sccwebsit...f/591f7dda55aa
d72a80256c670041a50d/55ade2860da4f0758025783200491a28/$FILE/Ops%20Guidel
ines%20-%20%20April%202011-March%202012.pdf

--
Mike D