Train passengers are suffering unfair penalties for minor and often genuine mistakes in buying tickets, an inquiry has found.

The Office of Rail and Road (ORR) said Britain’s fare system was “complex” and that rail firms must stop taking “disproportionate action” against travellers.

Sam Williamson, 22, thought he’d bagged a £1.90 discount on a ticket using his young person’s rail card, but was threatened with court action – now dropped – as the saving didn’t apply before 10am on weekdays outside of July and August.

The Rail Delivery Group, which represents rail firms, said fare evasion costs the industry £400m a year but acknowledged the industry has to be “more consistent”.

Susie McAdam, 26, was travelling from Stansted Airport to London. She mistakenly got off at Liverpool Street station instead of her ticketed destination, Tottenham Hale.

“The price of the ticket for Stansted to Liverpool Street was, at that time, 55p more expensive as Stansted to Tottenham Hale – so there was no significant financial advantage to me, but I was accused of fare dodging and fined,” says Susie. “It was a genuinely innocent mistake”.

She had to pay a penalty fare of £57 – reduced from £100.

“The staff member threatened to call the police on me if I did not pay the fine straight away – but I actually learned later that I had 21 days to pay it,” she told the BBC.

“This all happened late at night and it felt very threatening,” she adds. “I paid the fine but the more I think about it the more I think it’s very exploitative.”

The ORR inquiry looked in to how the rail industry handles fare evasion after passengers were being prosecuted over small amounts of money.

The ORR cited one case, which was eventually dropped when a local politician looked into the issues, where a passenger was threatened with court action for accidentally choosing a 16-25 railcard discount when they held a 26-30 railcard. Both give the same discount.

The report also found passengers who had forgotten their railcard were often penalised, though it said it was difficult for rail staff to determine genuine mistakes from those who chose to deliberately underpay.

James Bissell, 27, says he bought a ticket using his railcard and got a £1.30 discount. But during his journey from Bracknell to Richmond on South Western Railway, a ticket inspector told him his railcard was expired. He paid a £133.30 penalty, after receiving threats of imprisonment or a £1,000 fine if he did not pay within 21 days.

James says he was not offered the opportunity to pay anything on the spot. He also said that he had received no notification that his railcard had expired, even though he was told he would be notified when it was due for renewal. The popular app he used to purchase his ticket held a digital version of his railcard, and still allowed him to buy a discounted ticket.

“Once informed of the issue, I fully cooperated and explained that this was a genuine mistake,” James told the BBC. “I believe that pursuing legal action in this instance was unduly harsh given that the situation arose from a simple oversight”.

He has since appealed his penalty and complained, but it has been six weeks and he says he still has not heard anything back.

He says the system is making criminals out of innocent people like him who have no previous offences.

Rail Minister Lord Peter Hendy said “ham-fisted prosecutions” were punishing innocent passengers.

He added that the government planned on tackling fare-dodging by simplifying ticketing and developing plans for a state-owned rail operator, Great British Railway.

Sam said his “tiny” mistake “would translate to a prosecution, potentially, or hundreds [of pounds] in fines, so I could have ended up with a criminal record”.

He describes the way he was caught out as “slightly convoluted”, adding “we can’t expect a regular commuter to be aware of something that niche on a regular basis”.

ORR strategy director Stephanie Tobyn said the legal framework and enforcement of ticketing is “increasingly complex and appears weighted towards industry, leaving some passengers who make innocent errors vulnerable to disproportionate outcomes”.

However, she added that “fare evasion remains a significant problem, and rigorous action should be taken against those who intentionally seek to defraud the railway”.

The inquiry said evading fares was becoming a normal thing to do “among certain passenger groups” and that it is becoming “increasingly more challenging to tackle”.

Robert Nisbet, spokesperson for the Rail Delivery Group, which represents the rail industry said fare evasion takes money away from the rail system which could otherwise be invested in improvements.

He added: “We could be better, as an industry, we could be clearer, we could be more consistent across the country.

“We don’t always get it right, we acknowledge that, we have to be better”.