<P>In September 2001, the world witnessed the horrific events of 9/11. A great deal has happened on the counterterrorist front in the 20 years since. While the terrorist threat has greatly diminished in Northern Ireland, the events of 9/11 and their aftermath have ushered in a new phase for the rest of the UK with some familiar, but also many novel, characteristics.</P><P></P><P>This ambitious study takes stock of counterterrorism in Britain in this anniversary year. Assessing current challenges, and closely mirroring the ''four Ps'' of the official CONTEST counterterrorist strategy - <I>Protect</I>, <I>Prepare</I>, <I>Prevent</I>, and <I>Pursue</I> - it seeks to summarize and grasp the essence of domestic law and policy, without being burdened by excessive technical detail. It also provides a rigorous, context-aware, illuminating, yet concise, accessible, and policy-relevant analysis of this important and controversial subject, grounded in relevant social science, policy studies, and