The CAB are probably referring to the following in the 'Penalty Fares Policy' document, which contains guidelines that
TOCs▸ should adhere to when setting up and running a Penalty Fares scheme:
Where penalty fares apply, passengers must allow enough time to buy a ticket, including time to queue, if necessary. Under normal circumstances, passengers may still be charged a penalty fare if they join a train without a ticket, even if there was a queue at the ticket office or ticket machine. However, we expect operators to provide enough ticket windows, ticket machines and staff at staffed stations to meet the queuing standards set out in the Ticketing and Settlement Agreement and their Passenger^s Charter under normal circumstances. This standard is normally five minutes at peak times and three minutes at other times. If queues at a particular station regularly fail to meet these standards at certain times or days of the week, the operator must either take action to sort out the problem before a penalty fares scheme is introduced or make sure that passengers are not charged penalty fares when these queuing standards are not met. This might include providing extra staff or ticket machines. A penalty fares scheme must include arrangements for telling authorised collectors when long queues build up at ticket offices.
(Strategic Rail Authority - about)%20-%20Penalty%20Fare%20Policy%202002.pdf" target="_blank">https://www.ircas.co.uk/docs/SRA%20-%20Penalty%20Fare%20Policy%202002.pdf