At most stations there are ticket offices, ticket machines, and a Permit to Travel machine. The latter is to provide a permit on those occasions when the ticket office is closed. However, in the morning peak period at my local station, there is frequently a lengthy queue at the ticket office, a broken ticket machine, and a switched-off Permit to Travel machine.
At Charing Cross, however, there are many revenue protection staff, waiting to fine people for travelling without tickets. If British Rail was serious about selling tickets in advance of travel it could deploy some of the revenue protection staff at suburban stations to sell tickets, rather than penalise people for arriving without them.
London, SE6Reuse content