The UK government identified 'improving support within the criminal justice systems' as a priority for autistic people. There is a lack of quantitative research to enable policymakers to make evidence-based decisions on how to improve access to justice for autistic people. This study used a case-comparison design to compare the experiences of 145 autistic and 116 non-autistic adults who had been arrested at some point in their life. Autistic participants were nearly five times more likely to state that they were not given an appropriate adult even though they believed they needed one and felt less able to communicate with the police. Autistic participants felt less able to cope with stress, twice as likely to have experienced meltdowns and five times more likely to have experienced shutdowns because of their criminal justice involvement. We conclude that there are inequalities that autistic people face when navigating the criminal justice system and the degree to which they can participate effectively in the justice process. This has an impact on their mental health. Policy recommendations are discussed based on this evidence.