Bit harsh that RoaldoM. Obviously your personal opinion, but to class all road riders as idiots is a bit extreme. Most drivers slow down and give way without any fuss, even if they hate horses they want to stop their car being damaged by a possible collision. Agree though that there are some completely arrogant riders who behave badly on the roads and never acknowledge a driver who slows down, height of rudeness that.
In answer to your question Blackthorn, the only legislation is that all riders under 14 must wear a riding hat! Any adult horse owner/rider worth anything would make damn sure a child is competent and that the horse is bomb-proof, as police horses are trained to be, but unfortunately there are people in all walks of life that think they know best and can handle any situation, sometimes with awful consequences.