Research by the Office of Rail and Road (ORR) highlighted that several operators are not meeting its five standards of good practice.
- Greater Anglia not having a PDF delay claim form on its website
- Chiltern Railways not offering a dedicated online claim process
- Merseyrail not providing a dedicated paper claims form
- Transpennine Express not including a direct link to compensation information on the homepage of its website
- Caledonian Sleeper not producing a dedicated information poster or contact card.
The ORR acknowledged in its report that there has been "generally good progress" in implementing recommendations it made in March, following a super-complaint by consumer group Which? in December 2015.
But it warned: "In spite of progress there are also specific gaps that still need to be addressed."
Just 35% of passengers are claiming compensation for rail disruption, according to the results of a survey by independent watchdog Transport Focus published last month. This is up from 12% in 2013.
The ORR pledged to raise its concerns with train companies, carry out further mystery shopper exercises and work with the Department for Transport to make operators more open about compensation arrangements.
The regulator's director of railway markets and economics, John Larkinson, said: "It's clear the rail industry is committed to making improvements and the majority of train companies have updated their websites, claim forms and claim processes. However, some have only made minimal changes.
"We are calling on all train companies to adopt best practice, increase the number of channels available to claim compensation, advertise compensation rights and make it as easy as possible for passengers to claim."
A full report into how the industry is doing on its obligations to passengers will be published by the ORR in summer 2017.
Which? director of campaigns Vickie Sheriff said: "Train companies are finally starting to take long overdue steps to tell passengers what they are entitled to and how to claim, but one year on from our super complaint more needs to be done.
"It must be easier to find out how to get compensation and make a claim.
"The regulator should take action if train companies do not make progress quickly and the Government must introduce a new mandatory ombudsman so that passenger complaints are properly heard and resolved."
A spokesman for the Rail Delivery Group, representing train operators, said: "Everyone in the railway wants trains to run on time and when things go wrong we want to put them right.
"Train companies are raising passengers' awareness of their compensation rights, making it easier to claim money back and paying out more to delayed passengers - nearly £45 million last year."