Hi again Katy,
Well, he certainly has a lot going on there. I hope you have good support for yourself from family and friends as you try to figure this all out.

Just from reading your message, my suggestion would be to follow your instincts and ask for a multidisciplinary evaluation for Autism Spectrum condition if that's never been done. I'm no expert, but I was in a somewhat similar place myself years ago.

If he has mild developmental delay then that may have blurred the lines a bit and the only way to truly know is for him to undergo the right assessments if they've not been done. e.g. if he has difficulties with speech and language that may affect the way he communicates and doesn't necessarily mean he has autism so the professionals may be overlooking other things that you observe.

Frankly, when my son was finally correctly diagnosed it was total and absolute relief as so many things made more sense. Have you spoken to his Psychiatrist and Speech and Language specialist about your concerns that he may be on Autism Spectrum?

If he does have Autism, and he's diagnosed correctly and he's set up in the right educational environment with people who understand Autism in children and teens, then he can only flourish. It sounds as if he's struggling right now, so my heartfelt suggestion is to go with your gut feelings and if you feel he's not been diagnosed correctly or is not receiving particular modifications or direction educationally or medically, then go for it. The sooner the better if he is indeed on Autism spectrum.

I see you are in the UK...
What is Autism from Autism.org.uk

Diagnosis What to Expect

There are other links on that UK site that talk more about education and schools etc..

Education Schools

p.s. another thought. Sorry if there are too many questions, but I wondered who actually diagnosed your son with Tourettes Syndrome? Was it a Psychiatrist or Neurologist. I also wondered if he had any phonic/vocal tics as well as the motor tics you mentioned. e.g. List of Common Tics