IME the term 'semi-professional' is, for insurance purposes, pretty much a meaningless term. I've been out of the loop for around 7 years now though, so things might have changed in the meantime...
Just as a matter of interest, I'd be interested to know whether anybody has actually used that term when arranging their car insurance. If you did, how did they react? Serious question.
Just as a passing observation, having just read the entire thread I'm hearing hearing a lot of 'This is how the system works. No, really...' from one side and a lot of 'That can't be right, because...' from the other. Sweeping generalisation I know, but all the same...