Train passengers are 35 times more likely to complain about services than they are to praise them.
According to figures from The Office Of Rail And Road, London Midland Trains received 35.2 complaints per 100,000 journeys.
By comparison the company only received 1.0 messages of praise.
London Midland spokesman Francis Thomas said that the firm welcomed any feedback, positive or negative.
He said: “Feedback is how we continue to improve our customer satisfaction rate. Much of the £50million investment over the next year is based on what customers have said is important to them.
“It’s increasingly easy for customers to get in touch, not just by writing but by emailing or via our mobile phone app.
“We’d also encourage people to get in touch with complaints if their journeys have been delayed by 30 minutes or more. With the mobile apps you can now even do that while you are still on the train.”
Although London Midland had one of the highest complaint rates of any rail operating firm, it was still well behind Virgin Trains West Coast who had 144.1 complaints per 100,000 journeys.
London Midland runs services between Northampton and London Euston, with stops including Hemel, Berkhamsted and Tring.
The firm was one of the best at replying to complaints within 20 working days. 98.7 per cent of responses came within this time, comfortably beating the 95 per cent target.