Today I travelled from a unstaffed PF station to Leeds with cash, TVM at the station out of order, battery flat on board, therefore no choice but to buy on arrival at Leeds! It would be interesting to see how revenue protection would have reacted to that, a clear case of no opportunity to pay but is it down to me or them to prove the TVM was out of order and the guard had a flat battery? (I don't even think the TVM shows the time and date when it is out of order either!)
On the back of the ticket issued at Leeds
'PENALTY FARE WARNING If travelling from a Penalty Fare Station, on a Penalty Fare Train, you must buy your ticket (or get a promise to pay notice or Permit to Travel) before you board the train where ticket, or Permit to Travel or promise to pay facilities are available. If an Authorised Penalty Fares Collector had been checking tickets you may have been charged a £20 Penalty Fare or twice the full single fare to the next station stop, whichever is the greater. You must buy a valid ticket before boarding a train , if ticket issuing facilities are available'