When I helped my daughter buy a place, it is nearly always the smallest, what the builders call a bedroom, that is the problem with UK homes. They are not big enough to swing a cat in, as the expression goes. It is a gimmick. I think the UK should follow the US in that a room can only be called a bedroom, if it can have a wardrobe as well as a bed, well, that was said on one of those US doer upper shows, I maybe wrong.
Also headspace is another problem, in France, the floor space can only be counted when it is a certain height (something similar to a person standing).