The big question now is, What have we gained in terms of national security in return for the enormous price we have paid for counterterrorist law? There is no clear answer to this question.

It is possible that some of the provisions have been extremely helpful in curbing the threat. On June 15, 2004, MI5 placed under surveillance Dhiren Barot, also known as Abu Esa al Britani. The Security Services subsequently lost track of him, but when a laptop captured in Pakistan revealed his involvement in a terrorist plot, authorities decided to capture him as soon as he resurfaced – as he did, in August. A counterterrorist official later admitted, “It is no exaggeration to say that, at the time of the arrest, there was little or no admissible evidence against Barot.” But special powers of detention bought the state time to find enough material to bring charges; and over the next two years, careful examination of nearly 300 computers, 1,800 disks, CDs and hard drives, and other materials helped build a watertight case.