At Derby bus station this afternoon, a lady ahead of me in the queue to board Indigo back to Nottingham presented her ticket to the driver. The driver let her through after glancing at the ticket but after a second he called her back and said that her ticket was invalid in Derby. This came as a shock to the woman, who said she had specifically asked, when purchasing the ticket from another driver, if the ticket could be used in Derby; that driver informed her that she would be able to.
Fortunately, the driver on board Indigo was reasonable about it; he let the lady on without having to buy another ticket and said for future reference the ticket she possessed was not valid in Derby. I think this is a far more measured response than, say, stopping a bus suddenly, beckoning a passenger like a dog and making them leave.