The details of restrictions and easements is split across a few places
To find out when Off-Peak, Off-Peak Day and Super Off-Peak tickets are/aren’t valid, you need the National Rail Off-Peak ticket details PDF. It’s a large document, and you’ll need to do a lot of searching, but all the restrictions and easements are given in there to fight quite a bit with the National Rail Enquiries Online Journey Planner as they’ve removed the full PDF “to simplify their website”. On the “Times and Tickets” page, click “Other Tickets” then click the name of the ticket type under “Ticket summary”. Scroll to the bottom of and find the restrictions section, there’s a link from there to the exact rules of what times/trains the ticket is/isn’t valid for. eg from this search page
You get to this set of restriction details here.
In terms of working out what is by default allowed in terms of routes, you’ll want the ATOC Routing Guide – start with the introduction, the use that to work out which maps to use and how. To find out where the rules are relaxed, you need the ATOC routing guide easements PDF – again you’ll need to search to find your stations of interest.
Alternately, just ask at a ticket office – they’re generally experts at all of the above and will be able to look it up (fairly) quickly! Oh, and if you’re doing something that is allowed but is pretty unusual, it may be worth bringing the appropriate PDFs with you along with a note of the pages, to speed up ticket checks if the conductor isn’t already aware of a given route/ticket combo being valid…
Credit:stackoverflow.com‘