The investigation, carried out by BBC South East, found some tickets, including a season ticket from Gatwick to the capital, were being advertised for a third of their retail price, the Telegraph reports.
Tickets are being sold on the hidden part of the internet by a self-styled ‘Robin Hood’ group, which claims it is offering “an affordable public service”.
The investigation found that although the tickets do not allow customers through barriers at stations, staff allowed travellers through anyway because the tickets appear genuine.
The group, who were not named in the investigation, told the BBC “no one should be ashamed of getting one over companies like Southern Rail”.
A spokesperson for the Rail Delivery Group, which represents train companies, said fare dodgers “deprive” the railway of around £200 million per year.
People caught in possession of a forged ticket risk a “hefty fine” or even a prison sentence as it is a criminal offence, he added.
