I think that the whole issue from the companies perspective is trying to stay on the right side of the HMRC with respect to expenses re-imbursement. Unfortunately a lot of this is down to 'interpretation' which is not ideal as different companies have a different take on it, and then a lot impose their own extra rules on top. As I work remotely now all expenses are submitted by means of scans/electronically anyway, and when I buy an e or m ticket I submit the receipt from the purchase that I receive by email. This hasn't caused a problem
I have only twice had a problem in retaining ticket before everything went online, once at St Neots where the exit barrier retained my ticket, and there were no staff around, I had the return half, submitted that and got paid, and once at Manchester Piccadilly where I had an argument but got to keep my ticket.
Over nearly 50 years in industry I have found that the companies where the expense policy has been rigid, and more importantly, where legitimate claims are regularly refused actually have the worst rates of expenses fraud. Certainly I will not be left out of pocket if performing legitimate company business, and over the years have taken steps to ensure that I do not end up out of pocket on occasions where legitimate claims have been refused. Once people start making claims which ensure they are not out of pocket (morally correct, legally incorrect) its a small step for some to make totally fraudulent claims to make a profit. However try explaining that to a bone headed accountant who thinks he is saving money.
Ticket offices used to issue a receipt if requested, I don't know if that still applies, I can remember in my early days at work (mid - late 70s) you would get a hand written receipt with your small cardboard ticket for expenses if you asked.