Ask merika to explain it to you, matthew. Mind you at least she's consistent in that she's not anti-war. From memory, it has something to do with big guns, swamps and stamina
I must admit, I've not read about why this is necessary but assume it's part of the new package of mesures in reponse to 7 July attacks. Any new technology like this needs to be introduced with safeguards in place to prevent abuse and with it's implementation subject to regular, public scrutiny. It is a slow erosion of civil liberties, but the risk of abuse is small compared to say, the risk of terrorism. I thinik it's a necessary evil. We also have the right not to be blown up on the way to work, that's more fundamental than the right not to have anonymised data collected about our movements.