"....An obvious start would be to make the UAVs squawk like everyone else. (Something the size of a swallow may well be exempt that requirement IanC! - as long as any airprox's are still investigated and lessons learned)."
Not everyone squawks - there are a host of a/c that don't, including some of Her Majesty's finest. Similarly, there are many who don't carry on-board TCAS. UAVs are going to become a bit of a problem in the coming years.
Still, if you live around Swindon or Scouseport, there will be plenty of opportunity for some target practice using the police's UAVs