Which, of course, all sounds very complicated, but I am always happy to answer any questions anyone has to fathom out out rail network
A small addendum to Major WC's expert dissertation: you cannot usually reserve seats on 'local' trains. This is very confusing since some of these services run longer routes than some of the intercity routes on which you can reserve seats. So Helensburgh to Edinburgh is considered to be a 'local' service - no seat reservations - but takes as long as Glasgow to Carlisle on which you can get reservations as it is considered long distance!
