Ticket facilities
4.11 One of the SRA's three basic conditions for approving a penalty fares scheme is that passengers must be given a sufficient opportunity to buy a ticket or permit to travel before they get on a penalty fares train or enter a compulsory ticket area. Every penalty fares station must have sufficient facilities for selling tickets.
4.12 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 (see paragraph 4.33).
4.13 At staffed stations, operators must provide a second way of selling tickets in addition to the ticket office. This might be a 'permit to travel' machine or one or more self-service ticket machines. This is necessary because the ticket office may not be open at all times when trains are running, and there may be times when the ticket office is closed because of staff sickness or for other reasons. There may also be a need to provide back-up at busy times when queues might build up. Arrangements must be in place for the machines to be checked regularly by station staff and any faults put right quickly. Arrangements must be in place for any 'permit to travel' machine to be switched on when the ticket office is closed, temporarily unstaffed, or when long queues build up.
4.14 In exceptional circumstances, an operator may not need to provide a second way of selling tickets, if the ticket office is open at all times when trains are running and suitable arrangements have been made to deal with problems such as staff sickness, for example, through a system of stand-by staff who can be sent to any ticket office which does not open when it should.
http://www.dft.gov.uk/pgr/rail/legislation/pf/penaltyfarespolicya?page=5#a1019