Congratulations! I think you'll find widspread acceptance of autism and aspergers and US diagnosis, particularly in Oxford. The trick may be to ensure you meet up with the person responsible for pastoral issues/student well being so that he/she is aware of your needs and I'm sure you will not be the first person with these needs. Being such a good mix of people, I'm sure you'll be accepted for what you are, and you'll be able to participate in clubs, etc as much or as little as you want. When I studied maths there a good many years ago, I'd hazard a guess that 5 percent of us were on the spectrum, although it wasn't as well known/talked about then.