The rise of multiple legal systems in the same jurisdictional space has prompted a lively discourse on constitutional pluralism in recent decades. Although this debate was instigated as a result of the relationship between the European Court of Justice (ECJ) and Member State constitutional courts it has developed an international dimension after the judgment in Kadi. This paper considers the recent turn to ‘explicit judicial dialogue’ by the UK Supreme Court and the response of the European Court of Human Rights (ECtHR) in the Horncastle/Al-Khawaja saga. The explicit dialogue initiated by the UK Supreme Court in this saga may incorporate recognition of constitutional pluralism in the legal reasoning of UK human rights law. In doing so it may undermine the authority of both the UK Supreme Court and the legal system it serves. Section I of this paper examines the claims of constitutional pluralism and highlights judicial dialogue as the technique by which conflicting claims to authority are resolved in the European legal landscape. Section II applies the lessons of this critical exposition to the ‘open architecture’ of UK and European human rights law. It demonstrates the pluralist nature of the Human Rights Act 1998 and considers the manner in which the House of Lords took the case law of the ECtHR into account in its judgments. The reasoning of the House of Lords did not exploit the pluralist potential of the Human Rights Act but rather established a de facto hierarchical relationship between the ECtHR and the House of Lords. The establishment of the UK Supreme Court in 2009 gave the UK judiciary the chance to reassert themselves as an interpreter of the ECHR. Section III considers the Horncastle case, the leading judgment of the UK Supreme Court on the relationship between that court and the ECtHR, and the response from the ECtHR in Al-Khawaja. The Horncastle judgment is an invitation for an explicit judicial dialogue between the courts which may be disruptive to both UK human rights law and the Convention legal system. Section IV returns to the claims of constitutional pluralism to consider the extent to which explicit judicial dialogue may involve the incorporation of those claims into the system of reasoning of UK human rights law.