Below are some of my favourite books and websites on this topic. 

National Autistic Society - What is autism

Child Autism UK - Support, advice and services for children with autism - Child Autism UK - releasing potential

Autism Toolbox - Resources | Autism Toolbox

CAMHS - DOWNLOADS | CAMHS Resources (camhs-resources.co.uk)

PDA Society - PDA Society – Pathological Demand Avoidance – Part of the Autism Spectrum

These recommended books are linked to Amazon UK and may generate a commission which goes towards the costs of running this site.