National austitic society assessment

Hello,
im very new here and need some help. My brother was diagnosed with ASD on his 30th birthday.  We always suspected he was a little bit different but did not think he would not be able to cope living away from mum and dad.  He is the kindest person I know, he can drive and solve complex maths equations but lacks a lot of social skills and understanding.  He also has really bad OCD. He only managed to live away for a year and got into a lot of trouble. We managed to get him some housing and he has lived on his own for 1.5 years now but this has had lots of problems.
the council refuse to assess him.  It is all new to us and I was wondering if the NAS will assess, will the council accept their assessment and how much it costs for this ? All helpful pointers will be welcome.