Less than half of rail passengers who have complained to train companies believe they have received an adequate response, analysis shows.

Data from the rail regulator shows that fewer than one in five passengers on three particular operators – Govia Thameslink, Great Western and Northern – were satisfied with the outcome or handling of their complaints.

Even basic courtesy was felt to be lacking in some train operators: the majority of passengers who complained to Northern were not satisfied that the company had been polite in its response.

The latest full-year data, a follow-up survey completed by about 40,000 of approximately 500,000 complainants in 2017-18, showed that many companies had further alienated their customers in the way they had dealt with their complaint. On TransPennine Express and the now defunct Virgin Trains East Coast, 70% felt more negatively about the operator afterwards.

Consumer group Which? analysed the data and said it showed huge failings in the complaints process. Alex Hayman of Which? said: “Clearly there are serious underlying problems in the current rail complaints system, which need to be addressed. Train companies have to step up and start delivering good customer service when things go wrong: informing passengers about their rights and dealing properly with any complaints that arise.”

The rail industry announced earlier this year that it would appoint an ombudsman to oversee complaints that had not been resolved by operators, or on appeal to the independent watchdog, Transport Focus. The ombudsman is expected to be appointed before Christmas.

Anthony Smith, the chief executive of Transport Focus, said the watchdog had handled 7,000 appeals this year, about a third of which were for poor customer service. He said an ombudsman with legally binding powers “should help accelerate efforts by all train operators to improve their complaint handling”.

Paul Plummer, the chief executive of the Rail Delivery Group, which represents operators, said: “We’re committed to improving the service for our customers and to upholding the highest standards in our complaints process.”

Rail companies have improved the speed of their responses, with 93% of complaints closed within 20 working days, up from 88% the year before.