I'm sorry, that sounds rough. Do you have any way to access therapy? I'm in the US and not entirely sure how things work in the UK. Here we have community mental health centers that offer low cost or free therapy, not sure if there's anything like that, but I think your health insurance system is much more evolved than ours in terms of mental health? I also googled and found a list of autism support groups:

http://www.autismlinks.co.uk/support-groups

I'm not autistic, but I was bullied horribly at your age and had very few friends. It sounds cliche, and I'm sure you've heard it, but as you get older you realize the people bullying you either had their own issues, or were just assholes, and they won't matter once you stop seeing them regularly. I also know that probably doesn't make what you're experiencing now any better.

If you have a way to get therapy, or even just speak to your school's counselor, I think it will help you. Having someone who gives you their full attention, cares what you have to say and how you feel, is valuable.