ScotRail has been criticised for its "Byzantine" compensation scheme for delayed passengers, after research revealed the process is among the UK's most complicated.
Consumer group Which? said its study of online claim forms shows customers seeking payouts for disruption face a "fragmented and confusing" system.
The operators with the most complicated compensation processes were found to be Great Anglia, London Northwestern, ScotRail, Transport for Wales and West Midlands Trains.
Each demands 24 separate details before a claim can be submitted.
Which? found that customers are often asked for "seemingly irrelevant details" which creates "unnecessary barriers" to receiving the money they are owed.
Which's managing director of public markets, Alex Hayman, said: "It's clear this fragmented and confusing compensation system leads to people losing out on a lot of money when they have already suffered enough from unacceptable levels of delays and cancellations.
"The technology exists to deliver compensation automatically, but the industry continues to drag its heels, while benefiting from a system that deters passengers from claiming the money they are owed."
The scheme by ScotRail - owned by Abellio - has been described as "cynical" and triggered renewed calls for services to be owned by the public.
TSSA union leader Manuel Cortes said: "On top of suffering the worst punctuality and reliability since
Scotland's railways were privatised, now ScotRail passengers have to navigate a Byzantine claims process and provide 24 pieces of information in order to claim compensation for the delays.
"This is pure cynical greed. Abellio know that the harder it is for passengers to claim a refund the more likely they are to give up on the process."
Scottish
Conservative transport spokesman Jamie Greene said: "Obviously some level of detail is required to safeguard against fraud but it's hard to see how 24 pieces of information could be necessary.
"If ScotRail made it more straightforward it would much improve goodwill between them and passengers, something which is sadly severely lacking at present."
Scottish
Labour transport spokesman Colin Smyth said: "This is cynical stuff from ScotRail, given the thousands of passengers who will suffer from delayed, cancelled and overcrowded trains.
"Passengers shouldn't have to jump through hoops to get the compensation they are due for a shambolic service.
"Labour would bring our railways back into public hands so they work for passengers, not profits."
The firm's delay repay guarantee allows customers to be compensated when their journey is delayed by 30 minutes or more.
If anyone misses a connection because of that delay, they can claim for that expense too.
A ScotRail spokesman said: "We know how much of an inconvenience it is to customers when things don't go to plan, and it is only right that they are compensated when that happens.
"The delay repay system is easy to use and we regularly remind our customers to claim for compensation if their journey is delayed by 30 minutes or more."
