You would have thought that if this not-a-database of information was so valuable to stop terrorists they would have managed to stop the 7/7 bombings (and perhaps not shot and killed an innocent man). Funnily enough though they were caught completely unaware by the 7/7 bombings.
Since then I don't remember reading about any significant arrests or convictions of terrorists. There's been a few secret court cases and a few people arrested with potential bomb making equipment but in none of the cases did I get the impression they were really cracking a massive terrorist organization just some idiots that were probably more of a danger to themselves. I think we can be pretty sure that if we had managed to crack a large terrorist ring the powers that be would be shouting it from the roof tops.