Are terrorists criminals or combatants? It's hard to believe that almost six years after the attacks of 9/11 we are still asking that question. But we obviously are. Early on, this was recognized as a key question and we've muddled the attempts to answer it.
The answer has a huge impact on how we deal with terrorists. If they are criminals, then we investigate their conspiracies and crimes, rules of evidence apply, when arrested they have a right to trial, and when convicted can be released after serving their sentences. If they are combatants, we collect intelligence, rules of engagement apply, and when not killed, captured combatants can be interrogated and held until the end of the conflict.
Both approaches have distinct advantages and disadvantages, so up to now we've tried to hybridize our approach, often depending on where the terrorist choose to locate themselves. (Sometimes even where we have combatants route, we continue to muddle the distinction by using words like "suspected"... This hurts our efforts. We should use the military intelligence terms "probable" or "possible" when appropriate. Why not just say "enemy?") This approach allows the enemy to choose our rules of engagement/evidence and gives them an advantage.
The Brits have made a decision though "Let us be clear – terrorists are criminals, whose victims come from all walks of life, communities and religions. Terrorists attack the values shared by all law-abiding citizens. As a Government, as communities, as individuals, we need to ensure that the message of the terrorists is rejected.”
I think it's a bad choice, for many, many reasons, but at least it's clear. Now that you've made the choice - you better get to arresting some criminals. Before they blow up your cities.