I would posit that the reason there is no debate in Parliament is that MPs are afraid of what GCHQ / NSA / etc. might leak about them. What I find more worrying is that there is absolutely no debate about a) the fact British intelligence services have been compromised in the past and are still most likely compromised, imagine what a Kim Philby could do with all this data and b) the possibility of inserting false information into these data stores thus making even completely innocent people vulnerable to being blackmailed.