How to get an official diagnosis?

Hello everyone,

I need help on how to get an official diagnosis for full-time study at University, so I can obtain extra support.

Unfortunately I have no clue how to get an official diagnosis.

When I was 5 I was diagnosed with autism, however that was 25 years ago and my parents have no paperwork remaining to confirm this.

I previously tried my GP, but for some reason they don't seem keen to help.

Any advice on this matter would be brilliant. Thank you!