I just signed up purely to post a reply.
I’m 39 and from the uk too.
Over my life since I was a teenage I have been to my GP about the way my brain works and doesn’t work. That I struggle with things.
No doctor took me serious until about 15 months ago when I went to the doctor because I was really struggling after being given a new job managing multiple people and projects. Managing myself had always been a problem but this was something I could no longer mask or hide.
This doctor simply told me she wanted to refer me to the adult autism and ADD specialists in Sheffield.
Within 3 months of assessments and medication tests I was on a steady dose of Atomoxetine which without exaggeration has changed my life.
My relationships with people are better, I’m able to be more naturally focused, my career is going better than ever. And none of these effects are overt, they’re very subtle but impac every aspect of my life.
My advice would be if your Gp can’t help you then see another gP until somebody takes you serious.