How to get an adult ASD assessment

A psychologist suggested I look into ASD but was unable to offer any recommendations how to do so (and in any event I cannot afford to consult him again).  I asked my GP, who said, "You're talking to me on the phone, so you're not autistic."  When I attempted to challenge this, he just said the NHS couldn't help anyone with autism except the most severe cases.

So where do I look to for help?  I have of course found expensive clinics on-line, but I have no way to assess them and cannot afford them in any event.  How do I even get started?