Double Back, put most eloquently! It amazed me on an aero engineering degree course, how much of a struggle some students had grasping simple aerodynamic concepts that an eight year old with a rubber powered Sleek Streek would have learned after a few flights.
The current situation with multicopters is not that different to that of all the various small motorised vehicles which have been marketed in recent years (Mini Motos, Pit Bikes, GoPeds, Segways, engines for bicycles, etc.). Legislation already exists which covers their use on public roads with regard to licencing, insurance, MOTs & road tax, however the importers and retailers either hadn't made themselves aware of the rules, or chose to gloss over them to ensure they made a sale.
For drones sold by UK retailers, it would not be too much to insist that a sheet of paper was included in the top of the box which either summarised the relevant Air Navigation Orders, or directed the buyer to relevant CAA website (preferably a summary in layman's terms).
With regard to drones mail ordered from abroad, that is going to be more of a challenge to inform the buyers, although current publicity and a few test cases should filter through to would-be enthusiast's awareness.