"If someone could find a British metastudy containing a nice graph indicating ~50% of current standard medical treatments has no evidence of effectiveness, I would appreciate it - have had much trouble locating it."

I haven't seen that study, but if you look up any given common medical condition, for many of them there are studies about what percentage of those diagnosed are being treated in accordance with best practices. And for most conditions it's usually not more than a third. Doctors usually just prescribe whatever is advertised the most regardless of whether or not it's even remotely effective or safe, e.g. http://circ.ahajournals.org/cgi/content/full/99/15/2055