I'm going to controversial and probably get flamed.
Being a Yank expat in Britain, I read over the BHS requirements at one point, since I used to teach riding in the US and have considered doing it here, and perhaps, due to my outsider status (and from the West as well, which has a totally different horse ethos), have a more sceptical view of it than most Brits, who all seem very positive about the meaning of this qualification. There is a lot of useful information, helpful and necessary for those in the horse business, but acquiring this piece of paper not only entails a rather significant financial investment, but also your willingness to memorise a lot of completely arcane stuff and jump through a lot of hoops.
It just seems to be a part of this obsession with wanting to regulate everything, but I'm not convinced that the horse industry in Britain is a vast improvement over the horse industry in the US, where there is no such "quality control." Just like in the US, I've encountered huge variation with how barns are run, how people handle and ride their horses (the good, the bad, and the ugly), regardless of whether or not the individuals have a BHS qualification. I haven't taken a single lesson since I moved here, in part due to finances but also, I haven't seen one trainer I'd want to take lessons with, who really achieves and understands lightness and doesn't pull the horse into a frame with the inside rein (aside from videos of Carl Hester on YooToob). Not one. I'm sure they are out there, somewhere in the wilds of Britain, but I haven't come across any. If this is that hard to come by, what are people learning during the BHS training? Plus, my own background means that I approach training horses from a completely different angle.
That said, it still is a helpful hoop to jump through if you want to pursue an equine related career in this country. Being a cynical, opinionated, and from Colorado, I suppose I simply don't afford it the "holy" status that seems to be associated with it, as I've come across as many clueless people with BHS qualifications as without.