If torture worked, the need to criminalise it would be even more imperative than if it were ineffective because the temptation to use it would then be even greater. If torture did not work there would be no need to use it. It was largely because the CIA believed, or persuaded itself, that it did work that it became such a widespread practice.
Where to start with James Delingpole? I think it would be wise to begin where most people do, and judge this book by its cover. He is an archetypal political nerd, with a face which looks like an imploding sock-puppet held together with a thin wire frame. He sounds like he is gargling his own bile, which - listening to what actually comes out of his mouth - he probably is.