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Back to a Sovereign Future?: Constitutional Pluralism after Brexit

Published online by Cambridge University Press:  04 November 2019

University of Edinburgh


To the extent that the UK's decision to withdraw from the EU can be interpreted as a reassertion of the classic ideas of Westphalian sovereign statehood, it questions the relevance of constitutional pluralism as a resolutely ‘post-sovereign’ model of relations between state administrations and their supranational counterparts. This contribution will therefore examine the usefulness and relevance of the idea of constitutional pluralism after Brexit. It looks at the various features and relationships affected by the Brexit process analysing the relevance of constitutional pluralism to each relationship pre- and post-Brexit, concluding that, whereas Brexit clearly affects the different relationships involved, constitutional pluralism can and will remain relevant to EU/UK relations as well as within the EU, well into the future.

Copyright © Centre for European Legal Studies, Faculty of Law, University of Cambridge

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1 Neil MacCormick's writings on constitutional pluralism are primarily contained in MacCormick, N, ‘Beyond the Sovereign State’ (1993) 56 The Modern Law Review 1CrossRefGoogle Scholar; MacCormick, N, ‘The Maastricht-Urteil: Sovereignty Now’ (1995) 1 European Law Journal 259CrossRefGoogle Scholar; MacCormick, N, ‘Risking Constitutional Collision in Europe?’ (1998) 18 Oxford Journal of Legal Studies 517CrossRefGoogle Scholar; MacCormick, N, Questioning Sovereignty (Oxford University Press, 1999)CrossRefGoogle Scholar.

2 Walker, N, ‘The Idea of Constitutional Pluralism’ (2002) 65 The Modern Law Review 317, p 337CrossRefGoogle Scholar.

3 What MacCormick called ‘radical pluralism’. MacCormick, Questioning Sovereignty, note 1 above, p 117.

4 For example, Kumm and Maduro suggest that potential conflicts between EU law and state law can be resolved according to principles shared between the two orders. Kumm, M, ‘The Jurisprudence of Constitutional Conflict: Constitutional Supremacy in Europe before and after the Constitutional Treaty’ (2005) 11 European Law Journal 262CrossRefGoogle Scholar; Maduro, M Poiares, ‘Contrapunctual Law: Europe's Constitutional Pluralism in Action’ in Walker, N (ed), Sovereignty in Transition (Hart, 2003)Google Scholar.

5 Such as the norms of public international law in MacCormick's ‘pluralism under international law’; MacCormick, Questioning Sovereignty, note 1 above, p 117.

6 Walker, ‘The Idea of Constitutional Pluralism’, note 2 above, p 337.

7 Ibid.

8 MacCormick, Questioning Sovereignty, note 1 above, ch 8.

9 Amhlaigh, C Mac, ‘Late Sovereignty in Post-Integration Europe: Continuity and Change in a Constitutive Concept’ in Adler-Nissen, R and Gad, U Pram (eds), European Integration and Postcolonial Sovereignty Games: The EU Overseas Countries and Territories (Routledge, 2013), p 41Google Scholar.

10 N Walker, ‘Late Sovereignty in the European Union’ in Walker, Sovereignty in Transition, note 4 above.

11 Walker, ‘The Idea of Constitutional Pluralism’, note 2 above, p 338.

12 For an argument along these lines, see the contribution to the current symposium by Pech and Kelemen. In the political sphere, Commission President Junker's 2018 State of the Union speech to the European Parliament called for a ‘European sovereignty’. See ‘The Hour of European Sovereignty’, 2018 State of the Union Speech, at Also the European Parliament's chief Brexit interlocuter Guy Verhofstadt and French President Emmanuel Macron have come out vocally in favour of major EU institutional reform after Brexit. ‘Guy Verhofstadt: Brexit is a Golden Opportunity for the EU’ (Politico Europe 30 January 2017), at; ‘Macron Lays Out Vision for “Profound” Change in Post-Brexit EU’ (The Guardian 26 September 2017), at Also, serious discussion on an EU army suggest a similar trajectory. ‘Merkel Joins Macron in Calling for a European Army “One Day”’ (New York Times 13 November 2018), at

13 Van Gend en Loos v Nederlandse Administratie der Berlastingen, C-26/62, EU:C:1962:42; Costa v ENEL, C-6/64, EU:C:1964:34. The terms ‘supremacy’ and ‘primacy’ are used interchangeably in English. UK courts have, in the main, called it the ‘supremacy’ of EU law and this is the version which appears in the Withdrawal Agreement 2018 (see further below). However, as de Witte notes, the EU Courts have never actually used the term ‘supremacy’ and the only formal treaty-based recognition of the doctrine in Declaration 17 to the Lisbon Treaty uses the term ‘primacy’, which will therefore be used here. See generally de Witte, B, ‘Direct Effect, Primacy, and the Nature of the Legal Order’ in Craig, P and Búrca, G de (eds), Evolution of EU Law (Oxford University Press, 2011)Google Scholar. For a retelling and reappraisal of the well-known story, see Amhlaigh, C Mac, ‘The European Union's Constitutional Mosaic: Big “C” or small “c”; Is that the Question?’ in Walker, N, Shaw, J, and Tierney, S (eds), Europe's Constitutional Mosaic (Hart Publishing, 2011)Google Scholar.

14 See, for example, the UK Supreme Court in R(Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5, para 63.

15 As was made clear by Lord Bridge in R v Secretary of State for Transport, ex p Factortame (No 2) [1991] 1 AC 603 (see further below).

16 A position that was made clear in the Factortame judgment where Lord Bridge noted that ‘[u]nder the terms of the Act of 1972 it has always been clear that it was the duty of a United Kingdom court, when delivering final judgement, to override any rule of national law found to be in conflict with any directly enforceable rule of Community law’. Ibid, p 659.

17 From the perspective of the UK constitution. The European Court of Justice had, of course, developed its own view of the relationship between primacy and domestic constitutional law in its case law. See Costa, note 13 above; Nimz v City of Hamburg, C-184/89 EU:C:199150. For discussion see de Witte, note 13 above, pp 340–46.

18 Note 15 above.

19 See Elliot, M, ‘Sovereignty, Primacy and the Common Law Constitution: What Has EU Membership Taught Us?’ in Elliot, M, Williams, J, and Young, A (eds), The UK Constitution after Miller: Brexit and Beyond (Hart Publishing, 2018)Google Scholar; Gordon, M, ‘Brexit: A Challenge for the UK Constitution, of the UK Constitution?’ (2016) European Constitutional Law Review 409Google Scholar.

20 Thoburn v Sunderland County Council [2002] EWHC 195 (Admin), [2003] QB 151. For discussion, see Young, A, Parliamentary Sovereignty and the Human Rights Act (Hart Publishing, 2008), ch 2Google Scholar; Ahmed, F and Perry, A, ‘The Quasi-entrenchment of Constitutional Statutes’ (2014) 73 Cambridge Law Journal 514CrossRefGoogle Scholar.

21 As illustrated in Ellen St. Estates Ltd v Minister of Health [1934] 1 KB 590.

22 Thoburn, note 20 above, paras 68–69.

23 Ibid, para 45, endorsing Lord Denning's dictum in Marcarthys Ltd. v Smith [1979] 3 AER 325 where he found: ‘If the time should come when our Parliament deliberately passes and Act with the intention of repudiating the Treaty or any provision in it or intention of acting inconsistently with it and says so in express terms then I should have thought that it would be the duty of the courts to follow the statute of our Parliament’. Per Lord Denning, 329c–d.

24 R (HS2 Action Alliance Ltd) v Secretary of State for Transport [2014] UKSC 3.

25 Contained in the enrolled bill rule. See Edinburgh and Dalkeith Railway Co v Wauchope (1842) 8 C1 & F 710.

26 HS2, note 24 above, para 207.

27 Note 14 above.

28 Ibid, para 60.

29 Ibid, para 61.

30 Ibid, para 60.

31 Ibid, para 65.

32 Ibid.

33 Ibid, para 60.

34 Ibid, para 67.

35 Ibid, para 65.

36 As primarily expressed in the idea that no parliament can bind its successors. On continuing versus self-embracing sovereignty, see Hart, H L A, The Concept of Law (Oxford University Press, 1961), ch 6Google Scholar.

37 For discussion, see Elliot, M, ‘The Supreme Court's Judgment in Miller: In Search of Constitutional Principle’ (2017) 76 Cambridge Law Journal 257CrossRefGoogle Scholar.

38 Walker, NOur Constitutional Unsettlement’ (2014) 3 Public Law 529Google Scholar.

39 For a more in-depth exploration of this issue, see Dickson, J, ‘How Many Legal Systems? Some Puzzles Regarding the Identity Conditions of, and Relations between, Legal Systems in the European Union’ (2008) 2 Problema 9, p 4Google Scholar.

40 For an illustration of this possibility and other permutations and combinations of the relationship see Richmond, CPreserving the Identity Crisis: Autonomy, System and Sovereignty in European Law’ (1997) 16 Law and Philosophy 377Google Scholar. There is an alternative model of monism which Kelsen included in his account. That is that the relationship between international law and state law can also be viewed from the perspective of state law. The vantage point from which the single monist legal system is viewed is, therefore, a matter of perspective dictated by political or ideological considerations rather than a matter of legal logic. Kelsen, H, General Theory of Law and State (Harvard University Press, 1945), p 388Google Scholar. For discussion, see Vinx, L, Hans Kelsen's Pure Theory of Law: Legality and Legitimacy (Oxford University Press, 2007), ch 6CrossRefGoogle Scholar.

41 Dickson, note 39 above, p 4.

42 Perhaps the closest the UK Courts have come to adopting this position is Lord Denning's notorious comments in Bulmer v Bollinger, but even here the dominant influence of EU law is still predicated on the will of Parliament : ‘When we come to matters with a European element [EU law] is like an incoming tide. It flows into the estuaries and up the rivers. It cannot be held back, Parliament has decreed that the Treaty is henceforward to be part of our law. It is equal in force to any statute’. HP Bulmer Ltd v J Bollinger SA [1974] Ch 401, p 418.

43 As confirmed in statute in section 18 of the European Union Act 2018.

44 See, P-M Dupuy, ‘International Law and Domestic (Municipal) Law’ in Max Planck Encyclopedia of Public International Law (April 2011).

45 Ibid. To this extent, dualism has an affinity with ‘reverse monism’ whereby state law is hierarchical to international law when the unitary legal system is viewed from the perspective of state law. See Kelsen, note 40 above.

46 Miller note 14 above, para 65.

47 Walker, N, ‘Constitutional Pluralism Revisited’ (2016) 22(3) European Law Journal 333CrossRefGoogle Scholar.

48 MacCormick Questioning Sovereignty, note 1 above, p 117

49 As argued, for example, by William Wade. See Wade, WSovereignty – Revolution or Evolution?’ (1996) 112(4) Law Quarterly Review 568Google Scholar.

50 MacCormick, ‘The Maastricht Urteil’, note 1 above. For discussion in the context of HS2, see A Young, ‘Wilkommen zum Constitutional Pluralism’ (UK Constitutional Law Blog, 17 February 2014), at

51 For discussion, see Elliot, note 37 above.

52 Secs 2–4 WA.

53 Sec 7.

54 Sec 6(3) WA.

55 Sec 6(1)(a)

56 Sec 6(1)(b)

57 Sec 6(3) WA. With the important caveat that the UKSC will not be bound by any retained case law (Sec 6(4)(a)), but when considering whether to depart from retained EU law, it must apply the same tests it uses when departing from its own case law (Sec 6(5)).

58 Sec 5(1)–(2).

59 Albeit that it was recognised in a declaration to the Lisbon Treaty. See note 13 above.

60 See for example S Douglas-Scott, The Constitutional Implications of the EU(Withdrawal) Act 2018: A Critical Appraisal (QMUL School of Law Legal Studies) Research Paper No. 299/2019, at; P Craig, ‘Constitutional Principle, the Rule of Law and Political Reality: The European Union (Withdrawal) Act (2018)’ (2019) 82 The Modern Law Review 319; A Young, ‘Status of EU Law Post Brexit: Part One’ (UK Constititional Law Blog, 2 May 2017); A Young, ‘Status of EU Law Post Brexit: Part Two’ (UK Constitutional Law Blog, 4 May 2017), at

61 For discussion see A Young, ‘Status of EU Law Post Brexit: Part Two’ (UK Constitutional Law Blog,4 May 2017).

62 As envisaged by Part Four of the withdrawal agreement. See Agreement on the Withdrawal of the United Kingdom of Great Britain and Northern Ireland from the European Union and the European Atomic Energy Community [2019] OJ C384I/1 (12.11.2019).

63 Indeed, if it is the case, as many have argued, that much post-exit regulation developed autonomously by the UK will track EU regulation to a considerable degree, then the ‘shadow constitutional’ role that future EU law will play in the UK constitution could be even more pronounced. See, for example, discussion of the UK's wish to retain the EU scheme for data flows after exit in Craig, P, ‘Miller, EU Law and the UK’ in Elliot, M, Williams, J, and Young, A (eds), The UK Constitution after Miller and Beyond (Hart Publishing, 2018)Google Scholar

64 Sec 6(2).

65 Elliot, M and Tierney, S, ‘Political Pragmatism and Constitutional Principle: The European Union (Withdrawal) Act 2018’(2019) Public Law 37, p 44Google Scholar.

66 Ibid.

67 Ibid, n 35.

68 Sec 2 HRA.

69 For discussion of the various formulations and interpretations of the principle, see H Fenwick, ‘What's Wrong with s. 2 of the Human Rights Act?’ (UK Constitutional Law Blog, 2 October, 2012), at

70 R(Ullah) v Special Adjudicator [2004] UKHL 26, para 20, per Lord Bingham.

71 See Fenwick, note 69 above.

72 For discussion, see Amhlaigh, C Mac, ‘Pluralising Constitutional Pluralism’ in Roughan, N and Halpin, A (eds), In Pursuit of Pluralist Jurisprudence (Cambridge University Press, 2017)Google Scholar. Indeed, the experience with the HRA shows that a form of constitutional pluralism will also persist in the UK constitution through the HRA independently of EU law.

73 R v Horncastle & Others [2009] UKSC 14.

74 Ibid, para 11.

75 Al-Khawaja and Tahery v UK 15.12.11 (Applications nos 26766/05 and 22228/06).

76 For example, the application of constitutional pluralism internally to the UK's legal system based on different sources of law has been explored by Barber. See Barber, N, ‘Legal Pluralism and the European Union’ (2006) 12(3) European Law Journal 306CrossRefGoogle Scholar.

77 Some indication of the order of priority of retained EU law is provided for in the statute. For example, the Act distinguishes between two types of retained EU law—‘principal’ and ‘minor’. Moreover, minor retained EU law can be more easily amended than principal EU law. See Section 7 EUWA.

78 Especially if the EUWA is deemed to be a constitutional statute and therefore immune from implied repeal.

79 See Legislating for the United Kingdom's Withdrawal from the European Union (Cm 9446), White Paper (30 March 2017).

80 The surge in pro-EU support since Brexit has been well-documented. See ‘Brexit Causes Resurgence in Pro-EU Leanings across Continent’ (The Guardian, 8 July 2016), at Also, since Brexit, populist anti-EU movements in other Member States have subtly changed their rhetoric from demands for exit to demands for internal EU reform to satisfy their populist agendas. See A Clarkson, ‘Thought Populists Want to Kill the EU? It's Worse than that’ (Politico, 8 January 2019), at Even if these developments are still in their infancy, they do show that populism and euro-scepticism are not necessarily genetically linked and that an internal EU populism is possible.

81 See note 12 above.

82 See Kelemen and Pech in the current volume.

83 Walker, ‘Constitutional Pluralism Revisited’, note 47 above.

84 See Christiansen, T, ‘After the Spitzenkandidaten: Fundamental Change in the EU's Political System?’ (2016) 39(5) West European Politics 992CrossRefGoogle Scholar.

85 See Verhaeven, J, ‘European Integration and Finalité Politique’ in Liebscher, K, Christl, J, Mooslechner, P, and Ritzberger-Grünwald, D, The Economic Potential of a Larger Europe (Elgar Publishing, 2004)Google Scholar.

86 Such as that suggested by Commission President Juncker. See note 13 above.

87 For a recent examination of these issues, see Bellamy, R, A Republican Europe of States: Cosmopolitanism, Intergovernmentalism and Democracy in the EU (Cambridge University Press, 2019)CrossRefGoogle Scholar.

88 Walker, ‘Constitutional Pluralism Revisited’, note 47 above, p 352.

89 Ibid, p 352. For a similar argument applied to the legitimacy of authorities more generally, see Roughan, N, Authorities: Conflicts, Cooperation and Transnational Legal Theory (Oxford University Press, 2013)CrossRefGoogle Scholar.

90 Habermas, J, ‘Democracy in Europe: Why the Development of the EU Into a Transnational Democracy Is Necessary and How It Is Possible’ (2015) 21 European Law Journal 546CrossRefGoogle Scholar.