I have to disagree with manwithnofriends on this one. Getting a diagnosis, no matter what age you are, is worth it. I'm 27 and only got diagnosed this year (also in the UK). It was/is hard to come to terms with it since I'm not a child and it probably would have helped a lot more to know when I was growing up. Though that doesn't mean I'd never have wanted to know just because I'm already an adult.

I have a lot of difficulties with life on a daily basis. I've never known why a lot of my difficulties were so, but now I do and that makes a massive difference. Sure it'll never undo things from childhood, but it does still make a difference to who I am today. I now understand why I am the way I am, why I think the way I do, and why I struggle to interact with people around me.

Sadly for me to get a diagnosis, my life reached a rather critical point and I ended up having a bit of a break down and being taken to casualty and being assessed by an emergency PDoc. At the time, he wanted to commit me for a few days of observation but since he couldn't prove I was a risk to myself or others and I didn't want to stay, he couldn't.
He did however refer me to his superior who saw me the following week and after one hour with me she was convinced that the root of my problems came from AS, plus a side note of OCD and DID.

She then referred me to a specialist clinic in Edinburgh who carried out an assessment for AS specifically. The assessment lasted about 6 hours, involved a tonne of questions (like seriously, I've never answered so many questions in my life), she spoke with my mother at great length too about me as a child, about other family members etc. After that she conferred with her colleagues and a week later got back in touch to confirm that she was officially diagnosing me with High Functioning Autism/Aspergers Syndrome.

It's strange, but seeing that in writing provided me a relief that I can't actually begin to explain. Sure, it doesn't hand me a big fix or a magic wand to go back in time, but at least I know why now and that DOES make a difference.

As for the OCD and DID, well those aren't really quite as comforting to know about, but at least I know I'm not suffering from psychosis which is what the original guy was worried about haha.

For diagnosis in the UK I think you do have to go through your GP or a PDoc. You may be able to find a private clinic to save the referral, but that would involve going private and having to pay for it which could be quite expensive. The NHS tends to have longer waiting times, but at least you don't have to pay.

Also, a final note in reference to manwithnofriends post where he said about meaning he'd have to change and become "normal". That's totally not what my PDoc is working with me for. For one, there is no "normal" for the Human condition. My PDoc and the support groups I've seen, mainly focus on helping us to understand others around us, and to help our family and friends better understand us and our needs. It's not about converting people.