In article ,
Peter Smyth wrote:
So I think your second interpretation is correct and the Routeing Guide
does not have any power to ban you from using through trains or the
shortest route.

This FoI request seems to suggest otherwise:

http://www.whatdotheyknow.com/reques...l_rail_routein

The pertinent extracts:

Recently First Scotrail proposed changes to some local and middle
distance journeys involving the "Fife Circle" route that have been
approved by Transport Scotland. ATOC and Passenger Focus have approved
these too. Formal approval by the Secretary of State will shortly be
given and the changes incorporated into the NRG. Essentially these are
negative easements. [...] A negative easement however as in the
Scotrail application prevents for example, a journey from Edinburgh to
Rosyth (27 minutes and 14.75 miles apart) being made via Kirkcaldy
which takes over 70 minutes and is a trip of 52 miles which the
routeing guide would normally allow solely because it is a through
train providing the journey.