How to Join Adult Social Groups

Hello, 

This is my first post here and I'm a 19 year old university student in London. I saw on the main page that NAS has some adult social groups for autistic people and I was wondering how I can join? I can't seem to find any information on where they take place or how to sign up. Has anyone here joined these groups? 

Also I wanted to ask if a formal diagnosis is required to join. I have been referred by my GP for a full assessment but it looks like I will have to wait a whole year for an actual diagnosis. (I have been told by a few different doctors that I most likely am autistic and am diagnosed with ADHD, depression, anxiety and processing issues, these just haven't been put together yet lol). 

Anyway, help on how to sign up would be appreciated 

thank you everyone :)