Can John Reid protect us from terrorism?

Apparently, the Home Office has no knowledge on whether the individuals it has arrested and detained in the six months since August 2006 under the somewhat controversial "detain without charge" 2006 Terrorism Act have been re-arrested after release under that same Act. According to John Reid, "the police do not routinely collate information on re-arrests under terrorism legislation."

Now... I have to admit I'm a little confused by his response. After all, how can we be engaged in a fight against terrorists which requires lots of serious police powers to detain people, and yet not be making a note of when we detain the same person twice under those laws in a matter of just six months?
Image from The Spine