Roger Masterman: Reasserting/Reappraising Dualism

Dualism is considered a staple characteristic of the UK’s constitutional order. Recognised as a necessary derivative of the concept of parliamentary sovereignty, the notion of dualism is ‘based on the proposition that international law and domestic law operate in independent spheres’ and that interaction between those spheres is formally contingent – in the forum of the domestic court at least – on incorporation by statute.

The idea of dualism rests on an understanding of constitutional law which clearly demarcates the internal and external, and which draws a binary distinction between sources as applicable in the domestic context, or not. The majority judgment in the Supreme Court’s Miller 1 decision strikingly captured this division, with the language of ‘independent spheres’ (at [55]) providing little indication of the potential for interaction or overlap between the two bodies of rules (a suggestion which otherwise (even allowing for the European Communities Act 1972) sits uneasily with the majority’s dualism-defying characterisation of EU law as ‘direct sources’ (at [61]) of domestic constitutional law).

The more recent Supreme Court decision in R (SC) v Secretary of State for Work and Pensions uses rather more neutral terminology than that employed in Miller 1 – with the Lord Reed-authored judgment (with which all six of the remaining Justices agreed) describing ‘international law and domestic law [as] operat[ing] in different spheres (emphasis added)’ (at [78]) – in other respects, however, SC provides an unyielding defence of the formal dualism principle.

It is, the Court begins, ‘a fundamental principle of our constitutional law that an unincorporated treaty does not form part of the law of the United Kingdom’ [77]. So far, so orthodox. The obligation of the Courts, the judgment continues, under the Human Rights Act to consider decisions of the European Court of Human Rights – including decisions in which the Strasbourg Court may have considered the effects of international law – does not alter this position; courts may not import the requirements of unincorporated treaties via an indirect route arising out of the Human Rights Act (at [91]). ‘The … question is whether the Human Rights Act has given domestic effect to unincorporated treaties. Clearly, it has not’ (at [79]). Echoes of Lord Donaldson’s speech in Brind – in which the pre-Human Rights Act importation of ECHR obligations by the ‘back door’, when Parliament had ‘quite clearly refrained from doing so by the front door’, was firmly rejected – provide a sovereignty-endorsing tenor to the judgment.

The Supreme Court’s focus in SC is firmly on the hard question of when international laws – particularly treaty obligations – will or will not ‘affect the existence of rights and obligations under our domestic law’ [91]. At the level of basic principle, the judgment of the court is easy to defend. Is it striking nonetheless, that the judgment otherwise adopts such an oppositional tone in relation to the interplay between domestic and international laws.

The Court’s engagement with the grey space between incorporation and non-incorporation – in which judges might discuss or refer to obligations in international law as a means of comparison, contextualisation or argumentative fortification – seems intended to curtail judicial discretion. Recent judgments from Supreme Court Justices suggesting a closer (softly influential?) relationship between the domestic and the international are criticised for having given rise to a ‘misunderstanding’ (at [80]) as to the requirements of domestic law and identified as obiter and (worse) per incuriam. For the court, these judgments have veered too closely to breaking down the distinction which dualism seeks to uphold.

The reasoning in SC on this point rests on a distinction which is of technical, or methodological, importance to the maintenance of the sovereignty-dualism nexus. Unincorporated treaties do not have independent or freestanding (direct) effects in domestic law. Nor are they rendered (directly) deployable in domestic law by virtue of the Human Rights Act or having been considered – by the European Court – as relevant to its construction of the Convention; ‘… the European Court has not treated provisions of international treaties as if they were directly incorporated into the Convention itself’ (at [83]). As a result, the Supreme Court in SC strongly rejects the suggestion that a domestic court is competent to determine whether national authorities are in compliance with an unincorporated treaty (at [86]).  

The Supreme Court concedes that those same treaties, however, may have a degree of (indirect) influence in relation to a domestic Court’s assessment of the requirements of the Convention rights as given effect via the Human Rights Act (at [92]). It may appear slightly paradoxical to some that the Supreme Court suggests – in its discussion of Mathieson v Secretary of State for Work and Pensions (again, at [92]) – that while direct application of the UNCRC by a domestic court is constitutionally impermissible, substantially the same result could have been achieved in practice by placing greater reliance on a decision of the European Court of Human Rights in which the Strasbourg Court had utilised the UNCRC. The Court’s SC decision is concerned to uphold the methodology, as well as the substantive principle of dualism.    

But it is also in relation to these indirect effects that the Supreme Court’s decision in SC suggests an excessive curtailment of judicial flexibility in the use of unincorporated treaties. Lady Hale’s reference to the UNCRC in McLaughlin as ‘reinforc[ing]’ a decision otherwise taken on the basis of Articles 8 and 14 ECHR is – for instance – cast amongst those judgments contributing to the wrong turn the SC decision seeks to correct. In packaging this decision as contributing to the ‘misunderstanding’ the Court treats a supplementary reference to international obligations as a part of the problem prompting SC’s corrective. Surely there is a substantive distinction between a domestic court deploying the UNCRC as an explicit measure of legality (in the absence of statutory incorporation) and using it – as in McLaughlin – to bolster a conclusion already reached on the basis on the applicable Convention rights? If so, the distinction is somewhat elided in SC.

There is also much of interest in what the Supreme Court leaves unsaid. It is perhaps not surprising that we find no reference to Lord Steyn’s turn-of-the-century understanding that Parliament legislates for a ‘modern liberal European democracy’ – such sentiments are no longer à la mode. More surprising is the Court’s failure to acknowledge the dualism-softening effects of the ‘strong presumption’ recognised in – among other cases – R v Lyons (at [27]) ‘in favour of interpreting English law (whether common law or statute) in a way which does not place the United Kingdom in breach of an international obligation.’ (Though perhaps, under current conditions, the assumptions which underpin this presumption no longer hold as firmly as they once might.)

But while courts may adhere to the language, and the methods, of dualism, we might ask whether such stark dividing lines between the internal and external remain appropriate. For one thing, dualism – perhaps as SC illustrates – is an excessively blunt tool. Dualism allows for the presentation of international and domestic obligations in law as being clearly separated (even when – as in the case of customary international law – they may not be) and conceptually different (even when both should exercise a constraining force on government). The latter distinction in particular provided a basis (of sorts) for Brandon Lewis’ justification for the UK Internal Market Bill (as introduced) proposing a ‘specific and limited’ breach of an international agreement recently agreed between the UK and EU.   

Even in those circumstances in which facilitating legislation has given domestic effect to international obligations, the concept of dualism remains somewhat oppositional, drawing distinctions between external and internal norms which might outlast the former’s formal ‘incorporation’ into the domestic order. The taint of the external has seen – despite now over two decades’ worth of decision-making by domestic courts, and a clear trend towards critical engagement with the Strasbourg case-law – the Human Rights Act dogged by claims that it forces domestic courts to operate as local proxies for the European Court of Human Rights. Adherence to the formal niceties of dualism has not seen the Act, or its jurisprudence, shake persistent legitimacy challenges based on the extent to which allows external norms to permeate the domestic order.

The recent history of domestic application of ECHR and EU norms – though both the product of legislative direction – brought the international and the domestic elements of UK constitutional law into closer proximity, blurring the distinction between the two in the process. Human Rights Act jurisprudence cannot be coherently explained without reference to decisions of the European Court of Human Rights, and cannot be understood either practically or politically as purely domestic in character. While the UK’s withdrawal from the EU might, at first blush, be seen as providing impetus to a reassertion of dualism – and a step towards reasserting the integrity of the domestic (I hesitate to say parliamentary) processes of law-making – the products of the withdrawal process cannot be fairly described as reinstating a clarity to the division between international and domestic norms. Instead, a sizeable body of retained EU law now exists, a body of rules which is on any reasonable assessment ‘domestic’ only by virtue of those provisions in the withdrawal legislation which declare it to be so. The ‘domestication’ of this body of rules provides a route towards potential amendment, and supported spurious claims that Brexit was done at the point of the UK’s formal exit from the EU, but does not realistically capture the nature of the hybrid norms that now persist.

Unquestioning adherence to the notion of dualism unhelpfully inhibits discussion of the genuine interconnectedness of domestic and international laws; on the narrow view evidenced in SC it also limits the potential utility of international sources (sources which might otherwise be binding on the state) as tools of judicial argumentation. Nor can the binary distinctions dualism draws usefully account for the co-generative nature of laws in the post-EU and HRA contexts. Rejection of the ‘in/out’ distinctions that dualism draws in favour of a more sophisticated account of the relationships between the UK constitution and international law now appears overdue.  

With many thanks to Matt Nicholson, and the UKCLA Blog Editors, for discussions and comments on an earlier draft.

Roger Masterman, Durham Law School

(Suggested citation: R. Masterman, ‘Reasserting/Reappraising Dualism’, U.K. Const. L. Blog (7th December 2021) (available at