Commuters could be paying too much or risking fines on the capital's rail services because ticket machines are confusing, it has been claimed.
A report by the Office of Rail and Road with mystery shoppers which found that 13 per cent of rail users weee paying more for than needed.
A further six per cent were at risk of being fined after underpaying by choosing the wrong tickets for their journey.
ORR director of railway markets and economics, John Larkinson, said: "Everyone travelling by train should be able to buy the most appropriate ticket for their journey."
Britain's train operators should refund passengers who find they could have bought a cheaper ticket, the regulator said.
Anthony Smith, chief executive of transport user watchdog Transport Focus, said: "Ticket vending machines need to operate more like a human ticket clerk, steering people to buy the ticket that they want, rather than baffling them with too many options."