Some interesting comparisons of how the various rail companies compare with the amounts of complaints.
http://www.railtechnologymagazine.com/HS2/orr-reveals-passenger-complaints-decreasing-but-highest-on-virgin-west-coast/141744
For the full report, which was compiled by the Office of Rail and Road (ORR), click the following link which will cure you if you suffer from insomnia.
http://orr.gov.uk/__data/assets/pdf_file/0012/22116/measuring-up-annual-rail-consumer-report-june-2016.pdf