1. http://www.bbc.com/news/uk-england-hereford-worcester-349367...
EDIT: I'm not saying shooting the thing is the best idea (esp. given bullet trajectory and such), but what real, immediate options does an offended homeowner have here?
No. And, at least in the U.S., there is no such ruling. You absolutely cannot shoot someone just for trespassing on your property.
I know that where I live, Nebraska, the rare instance when someone breaks into a home and gets shot the homeowner is in the clear. There is often talk of "castle doctrine" but I don't really know what that means. I also don't know if the breaking into a home is the important part or if someone on your lawn waving a gun or knife around could be shot with legal blessing.
The Castle Doctrine doesn't, as far as I know, have a single clear meaning, but generally refers to rules that expand the circumstances in which a homeowner can use force (including deadly force) on an intruder to their home.
If the shooter from OP's link used a .22 or anything other than bird shot, then they are a real fool and a danger to everyone around them. Off the top of my head I'm inclined to think that the reach of a shotgun is probably about the right distance that ought to be protected, maybe a little bit further because of cheap optics.
I really feel the need to drive this point home, for obvious reasons: there is no such theory. You CANNOT DO THIS. You cannot shoot a trespasser on your land, just because he is trespassing. There has to be something else involved like reasonable fear of imminent bodily injury. The threat cannot necessarily be implied from the mere fact that he is trespassing. (It's clearly a different case if the trespassing is happening in your field in broad daylight v. in your bedroom in the middle of the night.)
Anything other than birdshot in this situation would be unacceptable, IMO, assuming shooting the drone is acceptable in the first place.