"The law and guidelines
The process of diagnosis will vary depending on where you live.
There isn’t one standard way for an assessment to be carried out, but there are guidelines that professionals should be following such as those issued by the National Institute for Health and Clinical Excellence (NICE). NICE Clinical Guidelines apply in England and Wales but may also be taken up in Northern Ireland after being reviewed. NICE Clinical guidelines have no formal status in Scotland.
Further guidelines for each country are described below. It may be worth letting your GP know that you are aware of the strategies, laws and guidelines relevant to the country you live in. If your GP does not want to refer you for an assessment you could show them the information about these to challenge their decision.
England. The Autism Act (2009) led to the government producing statutory guidance for adults with autism, which is called the autism strategy (England only), published in December 2010. The autism strategy says that local authorities in England must have a clear pathway of diagnosis for adults, meaning that you should be able to have a diagnostic assessment and your GP or local authority should be able to tell you how you can get this assessment."