Where do the instructions prohibit 'passing through' if that happens to be where the maps touch?
They don't explicitly prohibit that, but they do say:
HOW TO USE THE NATIONAL ROUTEING GUIDE
STEP 7
Identify the route to which the code(s) refers using the maps
Each code refers to a map. If a single code is indicated the route is via any
route on that map from the first routeing point to the final routeing point
without doubling back (passing through the same station twice on a single
journey).
Where a routeing specifies that a combination of Maps be used e.g)
ER+PN+BD, the route is via any route on that map from the first routeing
point to intercept point(s) for the next map without doubling back, then via
any route within that map without doubling back. This is repeated until the
final map is reached then via any route within that map until the final
routeing point is reached.
Example (e) - Darlington to Shrewsbury via permitted route ER+PN+BD. This
allows travel from Darlington to York via Map ER, York to Manchester via Map
PN and Manchester to Shrewsbury via Map BD.
ALL MAPS NEED TO BE CONSULTED IN SEQUENTIAL ORDER.
DO NOT USE THE MAPS UNTIL YOU HAVE FOLLOWED STAGES 1 - 6.
Presumably it would be possible to buy a Leeds- Blackburn single to "bridge the gap" between the point where the ticket ceases to be valid and where it becomes valid again, having 'notionally' travelled on map MH?
You could buy a ticket to "bridge the gap" however what I'd do is obtain an itinerary for the longer route, and then ask the guard if you have permission to go via the shorter route.
Guards will, in nearly all cases, allow
reasonable routes. If a guard believes a route is
unreasonable, the guard may declare it invalid (whether it is or isn't) and take it from there, or, more correctly, seek clarification from Control regarding whether it is valid or not. A small number of guards carry a copy of the Routeing Guide (and some ask on here and I've answered some queries via PM) but that is unlikely, so most would need to contact Control, unless they had good knowledge of the Routeing Guide. I suspect many will not do that and charge a new fare that can be refunded (or UFN that can be cancelled) if it turns out they were wrong.
I'd say that using the ticket via Burnley is
likely to be considered
reasonable by the vast majority of guards, however using the more convoluted route that is permitted via Manchester is actually at risk of being deemed unreasonable, despite being valid. A guard will not know it is valid (unless they've read this thread; which is quite possible on this route
).
If a passenger is on a
permitted route that is deemed
unreasonable (by the guard; of course it's subjective), then it can result in being charged a UFN which may then have to be contested, or sold a new ticket that then has to be refunded. On some occasions the Routeing Guide is then changed as a result. Many customers choose not to use routes that are permitted that are likely to be considered unreasonable because they do not want the hassle that can result, despite being in the right.
