Consumer group Which? has launched a "super complaint" over how the rail industry compensates passengers for delays.
It has formally requested that the Office of Rail and Road (ORR) investigates the issue and called for the process of obtaining payouts to be simplified.
According to Which? some 47 million passenger journeys were either cancelled or significantly late in the 12 months to March.
Most train companies offer compensation if services are delayed by at least half an hour, but a survey of 7,000 passengers found that only a third (34%) of those who may be entitled to something actually made a claim.
The poll revealed that just 36% of passengers remembered being informed of their rights to a pay-out after their last delay.
Richard Lloyd, executive director at Which?, said: "Current proposals to improve compensation for passengers are too far down the track.
"Even if an automatic compensation system was included in all new franchises from tomorrow, it would take until at least 2025 to cover the whole network.
"Millions of passengers are left out of pocket each year, so train companies must do more to put their passengers first and make rail refunds easier."
The consumer group carried out a mystery shopper exercise to ask "basic questions" on refunds at 102 train stations.
In just 18% of cases the person was given a "full explanation" of the conditions for claiming, while in 63% of visits they were not told they could request their compensation in non-voucher form, such as a cheque.
David Sidebottom, passenger director of independent campaign group Transport Focus, declared that the super complaint "throws a welcome extra spotlight" on the issue.
"Our original research showed that less than 15% of passengers entitled to compensation for poor performance actually claimed," he said.
"The main reason was that they didn't know they were entitled to and didn't know how to do it."
The ORR issued a statement which explained that the rail industry has recently taken "positive steps" such as signing up to a code of practice on providing clear information to passengers, but noted that its research shows "passenger awareness of how and when to claim compensation is low".
It added: "We will be assessing whether more could and should be done for passengers as we investigate this complaint."
Virgin Trains recently launched automatic delay repay for some tickets, but this has not been introduced by other companies which still use paper or online forms.
A spokesman for the Rail Delivery Group (RDG), which represents train operators and Network Rail, claimed compensation has become "increasingly generous and easy to apply for".
It insisted that train companies are doing "lots more" to inform passengers of their entitlement to a pay-out with announcements on trains, handing out claim forms, issuing email reminders and posting messages on Twitter.
The RDG added: "We never want our customers to suffer delays or disruption but when things do go wrong we want to put it right."
The Enterprise Act enables certain bodies to issue super complaints when it appears the interests of consumers are being significantly harmed. The ORR is required to respond to Which? within 90 days.
A Department for Transport spokeswoman said: "We are committed to improving compensation arrangements and it is happening. We've introduced new measures which ensure all new franchises make the claims process swift and simple, including through technology, resulting in a seven-fold increase in payments since 2011.
"Tough performance targets will also mean that operators must take steps to minimise delays and deliver better services for passengers, or face penalties."