Punctuality is still the biggest concern for South West Trains (SWT) passengers as complaints about late trains made up 41 per cent of all grievances last year.
Statistics from the Office of Rail and Road showed that overall complaints about the operator dropped by nearly 18 per cent, SWT had the second-lowest response rate of all operators, at 60.8 per cent.
Complaints about commuters being packed into carriages made up 7.5 per cent of the total.
A SWT spokeswoman said despite trains being "extremely busy" throughout the day, a National Rail passenger survey had shown 81 per cent of passengers were satisfied with the service.
She added: "We are investing and working hard to provide more space for more passengers and recently completed the £65million introduction of 108 additional and refurbished carriages, providing longer trains for many of our busiest services.
"We are now working with Network Rail and the Department for Transport to invest a further £800million to make further improvements and by 2019 we will be providing an extra 30% space for our passengers during the busiest times of the day."
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