Enhanced flexibility: Special regimes of closer cooperation in core state powers

This article looks at the overarching Treaty architecture on secondary law differentiation and investigates three special regimes of closer cooperation, which are modelled upon, but cannot be entirely reconducted to, the enhanced cooperation procedure of Article 20 TEU. These regimes operate within core state powers and introduce a layer of additional flexibility in some policy-specific areas. They are the Article 136.1 TfEU special procedure for euro-related legislation, the fast-track procedure for enhanced cooperation in criminal law and the permanent structured cooperation in defence policies. The article argues that the web of closer cooperation regimes in secondary law enlarges the remit of differentiation within the Treaties beyond the standard enhanced cooperation and adapts it to core state power policy domains. This increased flexibility expands substantially the likelihood of such differentiation instruments to be used in practice. Moreover, as it extends to the policy fields in which opt-outs are generally established and where differentiation is mostly needed and operated, this accrued flexibility can replace, or at least supplement, differentiation through primary law derogations.