But what about fares where there are both period and Day returns...
[snip]
Off-Peak Day Single: ^9.40
Off-Peak Day Return: ^9.50
Off-Peak Return: ^18.10
That seems fairly fair to me.
Hmmm ... I disagree, I'm afraid. If I travel from Plymouth to Penzance off-peak, and back by a train the same day, it costs 9.50 ... but if I stay overnight and travel back off-peak the next day it costs 18.10. What possible justification is there for charging me nearly twice the amount for the return trip because it happens to be made a few hours later?
Perhaps I should have gone further in my original post / support of returns being around 60% of singles, and suggested that there should not be a day return - rather a period return that's valid for [time to be discussed - 8 days to 1 month].
I have seen arguments earlier that it's hard to check return halves on short journeys, so they're just for a day. But if the price of the return half goes up from 10p to five pounds, then you're not going to have the issue of lots of long-dated 10p tickets which would both tempt people to try it on, and at the same time cause staff and other travellers to get really upset about a potential fraud of travelling a day late. A good way to stop a potential fraud is to redraw the system so that it's no longer worthwhile to do it - far better than fussing over enforcements on 10p fares!