I'm not suggesting hiding JBs is good practice - merely stating that at least the plumbers have some proper guidance on what is considered "accessible" in their industry.
Regarding loft spaces, everyone I look in seems to have 18" of fibreglass insulation covering pipes, cables, downlights & LV transformers. I for one don't remove it all in the search for JBs that may or may not be there.
However, there must be literally millions of round JBs hidden in the UK domestic sector, with only a small percentage causing any problems. The test part of the I&T usually shows up any problems, then the fun begins.