Travelling back from Farringdon to Horsham earlier this evening on the return parts of my split tickets, when I arrived at Horsham and rummaged in my pocket for the Three Bridges -> Horsham ticket I couldn't find it, which means it had fallen out of my pocket when on the train (probably when I was getting my phone out). I was fortunate that (unusually) the barriers at Horsham were open so I could exit, but if they had been closed, would I have had to buy another ticket, or would it have been possible to convince a nearby member of staff, using the three paper tickets I still had and which were labelled as off peak day return, that I had lost the second section of my split and I was not trying it on?