The relational principle of parliamentary sovereignty

Parliamentary sovereignty is perhaps the most important principle in UK constitutional law. However, some of UK Supreme Court's most significant constitutional jurisprudence of the last decade sees that principle being put to uses and given meanings that are novel and, often, expansive, exposing the principle's flexibility and the Court itself to criticism. This article, centring on the novel accounts of parliamentary sovereignty offered in Privacy International, Miller II and UNCRC, explores the different ways in which that principle is understood by the Court and, particularly, the way the Court appears to conceptualise parliamentary sovereignty's relationship with other constitutional principles. This article offers three different models for making sense of the way the Court describes parliamentary sovereignty in these cases. It argues that these models illuminate, at a deeper level, three different underlying visions of the constitution which respectively postulate sovereignty as something that (a) overpowers other constitutional principles, (b) constitutes a threat to other principles (requiring the management of that threat), and (c) sits in relationship with other principles as part of a normative network. The article argues that the Court's presentation and mechanisation of parliamentary sovereignty is most effective when, and to the extent that, it takes full account of the relationship – including both its dissonant and consonant aspects –a between the sovereignty principle and the other constitutional principles with which it should properly be understood as interacting.