Since I?ve moved out of London, I will often find myself on quieter branch lines where people hop on for a couple of stops at a time. According to the conductors on those trains, if you board without a ticket the onus is on you to find the conductor and offer to pay. I?ve seen loads of people ?caught? by this and the conducters usually show no mercy Then again, I?ve usually been listening to the same people boasting about not paying for the 5 minutes previously so my sympathy is fairly limited