Originally Posted by
Ldnn1
[...]
I had no idea there was such a rule! As you suggest it can for all intents and purposes can be ignored, as you're extremely unlikely to be asked to move from an unreserved seat.
Just to prove I'm not making it up, this rule does feature in the
Advance ticket terms & conditions.
But I'd treat it much like the widely ignored
"Dogs Must Be Carried" rule, which is problematic for the majority who aren't travelling with a canine...
On a wider note I often sit in a reserved seat when I don't have a reservation - obviously only when the person for whom it was reserved isn't sitting in it (either they didn't catch that train or are sitting elsewhere).