Background This paper reports on the development of child and adult Action Plans for Autism Spectrum Disorder to address the problem of delayed diagnosis and lengthy waiting times. Evidence used in the development of action plans was gathered from a sequential mixed methods study to further understand the reasons for the long waiting time and potential solutions. This is the first published investigation, from the perspective of diagnosing professional teams, of the reasons for delays, which also generates solutions. Methods Ninety five clinicians from 8 child and 8 adult services attended 16 focus groups to explore clinicians’ views on a) reducing the wait for diagnosis and b) providing a good quality diagnostic process with good adherence to clinical guidelines. During focus groups, quantitative data were fed back, used to frame discussions and facilitate solution focused action planning with each service. Sixteen local action plans were synthesised to create an ASD Action Plan for children and an ASD Action Plan for adults. Results Key solutions are proposed to support the reduction of the wait for diagnostic assessment, through reducing non-attendance rates, reducing inappropriate referrals, developing efficient working and communication and improving the effectiveness of care pathways. These are presented in actions plans for use by clinical teams. Conclusion The first step in addressing the clinical challenge of increased wait for diagnostic assessment of ASD is understanding the complex and multi-factorial reasons for delays. The action plans developed here through systematic enquiry and synthesis may provide clinical diagnostic teams with evidence based guidance on common challenges and solutions to guide future quality improvement programmes. Future research to evaluate whether using Action Plans leads to a reduction in waiting times would be of value.