Yorkie
Let me give you a fiddle as old as time.
Travel without getting your outward ticket stamped or cancelled and then next time you travel use that and only pay for one way. Better still as long as the outward is valid then keep using it. This is one of the reasons that BR went to day of issue validity in many cases.
Another example that isvalid is the case of a Milton Keynes Central to New St ticket. This is cheaper (certainly was last time I had any dealings) than the corresponding reverse journey. So a again a fiddle is to buy the ticket and use only the return portion for the outward journey. THAT is yet another example of why the rule is there and I can see no hardship for that being the case.
Because tickets are priced selectively for flows this situation can arise. Again it is a potential source of abuse and loss of revenue to the Railway. Until there is a cast iron means of preventing fare evasion, then it is necessary to put up with such things. You cannot achieve a perfect world out there but I sometimes feel that you neglect to think about the other side of the argument. I think I know you well enough to say that without you taking offence.
Just because some people may fiddle things, doesn't mean that other people should be penalised when not fiddling, but not being aware of rules that are published in a location not available to the public.
If you were arrested tomorrow for accessing RAILUK forums, would you complain? of course you would.
"But people use the RAILUK forums for to learn how to split ticket, and we've written a new law banning its use."
"Where is that law written? Oh, its in our secret book, you aren't allowed to see it"