Types of flexibility – Tension: demands for diversity v. logic of uniformity – United Kingdom and differentiation under Maastricht and Amsterdam – Court of Justice (77/05 and 137/05) on Articles 4 and 5 Schengen Protocol: a clear signal disapproving UK's ‘pick and choose’ approach – Lisbon Protocols: unparalleled possibilities for differentiation coupled with coercive procedural constraints and threats of ‘expulsion’.