Hi,
On the website it states Alton Towers as a suggested place to go, I went last year and they have changed their disability policy and having an official statment of diagnosis is no longer enough. So unless you have a blue badge then you would need to provide a doctors letter stating you are unable to queue and your local doctor can charge upto £50 for this.
By the way this seems to be for all merlin theme parks, and when you read the T&Cs they are going the opposite way to being disability friendy.
They obviouly don't understand the traits autism as otherwise they wouldn't ask you to provide a doctors letter.