Steve Shaw: You can't shoot them down, you can't net them. Too dangerous. But you can bet your life that there's technology that won't let them fly where we don't want them flying and/or that can take over the controlling of them. And no, you can't have your bloody ball back.

There is "geofencing" technology available, and used in many off-the-shelf drones, to prevent them coming within a specified distance of a specified location. But this is easily overcome. And it's very easy to self-build a UAV controller that doesn't incorporate geofencing. My own company does it. Taking over control is not straightforward either....not that it would be much use with an autonomous drone.

Jon Freeman: I’m more interested in drones that can follow a flight path autonomously. Perhaps I’m missing something but it looks to me as if one, even with consumer grade stuff, could say program a drone to say make a short flight, circle round a target area a few times to get attention and return to base without the need for any communication between drone and base. I guess that if this method is possible, it would render any jamming technology useless? Or perhaps they could knock out the GPS signals it would need?

Yes, absolutely. Freely available software such as "Mission Planner" allows you to upload a pre-programmed flight path into a UAV which it will follow without any need for an external controller. We use this all the time to fly aerial survey missions looking for unexploded ordnance (aka explosive remnants of war) in areas of conflict.

Jamming GPS signals is possible, but not selectively....you'd have to jam over a significant area, causing a major issues to other applications using GNSS....not least to aircraft!