On two occassions I have had near misses with large RC model aeroplanes. Both times, the model only became visible when at very close range (not more than 100m), at the same height and directly in my 12o/c, resulting in me having to make very aggressive emergency breaks to avoid collision. I have seen at first hand many times the damage that a small bird can cause and so I would hate to think what the outcome might be of hitting a much larger, heavier and harder model. Dense components like batteries and engine blocks would almost certainly penetrate the cockpit, even at light aircraft speeds, and I am sure could cause significant damage to airframe and aircrew.
I hope that the police will exercise some airmanship when operating these UAVs, but that might be a bit much to expect from your average bobby with no aviation experience. A good rule to start with would be to get the thing on the deck as soon as any aircraft can be heard in the vicinity. I also expect that as soon as the get their hands on these toys they will want to use them anytime, anywhere and in any weather. I don't think the rural bad weather promise will last long.