This organisation is trying to challenge the shortcomings in the CMS (and seems to be the one who started the petition linked on here recently, for a public enquiry). Although they are collecting data via surveys, which might help them argue the case, just be mindful of keeping your details private if completing a form - I assume there's an option to complete it anonymously.
Home | CMS Watch.org
CMSWatch.org constitutes a committed collective, united by shared experiences of the shortcomings of both the Child Support Agency (CSA) and, since 2012, the Child Maintenance Service (CMS).
www.cmswatch.org