Given that it's already possible, and even routine according to Wacky Jacqui, to use comms data to determine a persons network of interest, and given that it's also already possible, with the requisite warrants to intercept the communications of those networks in real time, what's her (presumably not actually her, but some cadre of techno fetishist spooks) hard on for all this ?
OK, I get that the explosion of IP traffic has put a bit of a crimp in Cheltenham's style, hence the desire for all the new black boxes (I don't know how much the existing ones are able to look at IP traffic, I'd guess they were designed for other types of comms), but OTOH if TPTB go to an ISP, with a warrant, they can already get access to the IP traffic, and I'd be willing to bet it can be done in near real time.
There's just no reason to have all of this shit centralised unless you intend to mine the data. Mining the data will produce gibberish, leading to (even more) massive injustice.
Certainly, any such system will produce a crop of likely looking terrorist wannabes, it would probably have caught the idiot who thought that you can make bombs by dumping nails in plastic bottles full of "kerosene". But guess the fuck what ? He was already on the watch list. So just where are all the atrocities we could have stopped with such a tool ? Conspicuous by their absence. I for one would rather spend the 12Bn on something that might actually have a purpose other than traipsing an increasingly unlikely chorus line of fantasists, social inadequates, the mentally ill and the merely disenfranchised through the courts on trumped up "terror" charges.
Because the ones who really terrify the spooks, and the ones who actually frighten me a little, are the ones with proper funding, proper training, and proper opsec. Who know how to use payphones and old fashioned codes, all the arcana of tradecraft.
And you won't be able to stop them by building a fucking database.
In fact, since the HO and it's spooky masters seem to have been spending rather a lot of time watching catch up episodes of "Spooks" in preparation for the new series, let me respond in kind by outlining a threat drawn directly from the plot :
Bad Men With Guns (BMWG) wish to infiltrate UK and do Bad Stuff (BS), In the episode to which I'm referring, BMWG find out who MI5 are watching by nicking the watch list and send some of them on a sham suicide mission so that MI5 are looking the other way and fail to spot BMWG doing BS until it's (almost!) to late.
Now that's fairly contrived, involving, as it did, not only a Mossad mole in MI6, but a massive false flag recruitment of potential jihadis by said agency, etc, etc.
With an uberdatabase it would be oh so much easier to set up a shit load of false positives that absorb sufficient spooky resources to allow BMWG to waltz in under the radar and commit the One True Atrocity that (presumably) keeps the scenario fluffers up at night.
12 billion quid is a shit load of money to spend to bang up a few wankers who are probably already "on the radar", and it won't stop "real" terrorists, or even intelligent dilettantes, if they sit down and think their opsec through properly.
12Bn quid spent on road safety ? Public transport ? Health ? Education ? Or even, (ZOMGWTF!!!!) basic fucking scienctific research, or a space program to call our own ?