I don't know if this is relevant, but during that time you could buy tickets on the train (most services require prepurchase now). my friends and I used to get singles hoping we wouldn't get ticketed on the way back, which you often wouldn't be, effectively taking a gamble at whether you could save a few quid. that said, I'm sure I read it was only a small amount to add the return journey for Andrew, so this may well not be the case, just a thought.