Hobby Vs Business dilemma

Under the guidelines on the HMRC website you are probably not trading if you don’t plan to make a profit.

“You’re probably not trading if you sell some unwanted items occasionally or you don’t plan to make a profit. You can’t use any losses you make as part of a hobby to reduce your tax bill.”
So, that pretty much describes my intention. I have a full time job and only want to sell items I’ve made in my spare time to cover the cost of materials used i.e. No Profit.

However, I read somewhere that merely selling an item on eBay constitutes an act of ‘business’ and could void home insurance! So I searched around for Home Business insurance and the quote I found was cheaper than my current non-business home insurance, so naturally I signed up. So I’m covered either way. But now this raises an interesting dilemma. I’m wondering if HMRC could use that fact that I have Home Business Insurance as evidence that I am actually trading?
I should note that I have yet to sell any items, I am purely at the hobbyist stage but I was hoping that someone could provide a definitive answer on this.

Who gets the final word on whether you are trading: HMRC or insurance companies?