An answer to the OP is that in the UK it would be down to the civil police (who also use these) to counter them as the civil police have primacy.
The micro RVP would not need some form of explosive on board to be able to be used for terrorism, but I'm not going any further on that.
A local criminal uses one of these to check for police observation teams on his land. It is much cheaper and less obvious than the microlight that used to be employed for this task (day time only, and a hand held thermal sight is still used at night). Green posters may well remember just how important it is to keep your head down, or mask any OP activity, but it seems the police just can't get into this habit and stand out like sore thumbs at night.