The flexible formula of the British Constitution results in a relative openness to external influences. Notwithstanding this fact, the United Kingdom’s (UK’s) membership in the European Union’s (EU’s) structures (1973–2020) resulted in a progressive limitation of the doctrine of parliamentary sovereignty. Brexit will not reverse the effects of the ‘soft’ modification of the foundations of the UK’s system, which occurred in the sphere of the practical implementation of the competencies of the branches of governance. Prima facie, the decision on the UK’s withdrawal from the EU should result in a ‘renaissance’ of the traditional doctrine of Westminster sovereignty, per A.V. Dicey. However, judicial activism, continued validity of the European Convention on Human Rights (incorporated on the basis of Human Rights Act 1998) and the irreversible consequences of the devolution of competencies in the UK for Wales, Scotland and Northern Ireland are the factors that hinder the possible revitalisation of the sovereignty of the British Parliament.

In recent years, the United Kingdom has seen a growing doctrinal discourse around competing models of legal and political constitutionalism. The situation has been exacerbated by ongoing changes in both theory and practice, which have engendered a strong conviction that the UK is now departing from the political constitutionalism associated with the traditional model of parliamentary sovereignty, in which Parliament’s legislative power is unlimited by law and the courts have no right to question the validity of laws on substantive grounds. From a theoretical point of view, legal constitutionalists contributed to provoking this change while desiring to continue to promote it by moving almost completely and exclusively towards legal constitutionalism, thus supplanting its political formula. From a practical point of view, however, one should bear in mind that the events that led to a specific change in thinking about British constitutionalism encompass, in particular, the legal consequences resulting from the UK’s membership in the European Union, including the phenomenon of the so-called judicial activism. Nevertheless, these events were also induced by the expansion and strengthening of judicial review of administrative actions, judicial shaping of the principle of legality, as well as by the enactment and application of the Human Rights Act 1998.