Fair point about distinguishing between GCHQ and 'lower level' access to the data, I accept that distinction, and the risk of 'wrong hands' getting hold of it.
The trouble for me is, I feel an awful lot of our data has already fallen into the wrong hands, and will continue to do so every day, perfectly legally. I refer to organisations such as Google and other online data-collectors, and also the likes Supermarket data collections, insurance databases and the likes.
I'm not suggesting that two wrongs make a right but as long as we are where we are with commercial data-mining, I just feel it's all a but of a lost cause... So if the data is useful to police, I'm not too resistant to them having it too. I find it surprising if people trust Google and the supermarkets, as custodians of our data, more than they trust the police and the government.