Why cant we monitor lower airspace for potential intruders more effectively? Like many have pointed out above we face not just low flying aircraft, but now UAVs, or drones or paragliders or whatever.
Is it that difficult? Is it cost against likelihood? Granted we couldn't do the whole UK but how about from the Lizard to the Wash, or Humber even?
The Israelis have a whole lot less airspace to defend and a lot less airfields and even so, intruders still get through. As for the big picture, recording radar data is standard practice within ASACS and NATS who have their own low level surveillance radars. Any form of QRA may fail to catch the crooks on the ground, but the evidence of their actions is sitting on a Tape or hard drive at NATS or one of the CRC just waiting to be impounded as evidence for the court case and of course to ID the crooks in the first place after one of POBJOY's 'eyes' on the ground makes the initial call.