The constitutional implications of Brexit: Who is sovereign now?

The real-world power of the executive and legislature has been substantially diminished by Brexit, writes Miranda Butler

The Vote Leave campaign invited the public to 'take control' by voting to withdraw from the European Union. Brexiteers were offended by the power of EU institutions to pass laws which could overrule those made in the UK and argued that a vote to leave would make parliament sovereign once again. But has the Brexit vote made the UK parliament sovereign, as was promised, and, if so, what is the nature of such sovereignty?

The formal process of withdrawing from the EU will be triggered, of course, through the mechanism contained in article 50 of the Treaty on the Functioning of the European Union (TFEU). Article 50(1) provides that: 'Any member state may decide to withdraw from the union in accordance with its own constitutional requirements.' There is a general consensus that the UK's constitutional requirements mean that the actual triggering of article 50 will be carried out by the government using the treaty-making prerogative of the Crown.

A more controversial question is whether the UK's constitutional requirements demand parliamentary approval for the government to trigger article 50. I suggest they do.

Parliamentary sovereignty was at the heart of the Lleave campaign. It would be profoundly ironic if, having voted to take back sovereignty, so as to ensure parliament is the UK's supreme legislative body, the legislature were excluded by the executive from the process of triggering article 50.

Furthermore, following R v Secretary of State for the Home Department ex parte Fire Brigades Union [1995] 2 AC 513, the prerogative cannot be used to frustrate the will of parliament as expressed in primary legislation. Thus, triggering article 50, which would in effect nullify the European Communities Act 1972, must as a matter of constitutional necessity require a vote in parliament and, in all likelihood, primary legislation.

If this argument is correct, it will mean that another prerogative power, like the ability to declare war, has become subject to the prior approval of parliament. This would shift the focus of our constitution further away from the 'elected dictatorship' of the prime minister, wielding the Crown's prerogative powers, to a more democratic model asserting parliament's sovereignty. So far, so compatible with the desire to 'take control'.

Does the newly reinvigorated sovereignty of parliament mean that it has greater power than before? While parliament's constitutional status may be enhanced, I suggest that the real-world power of the executive and legislature has been substantially diminished.

Even with the triggering of article 50 still a distant prospect, Northern Ireland and Scotland have gained greater status from their threats of independence. Our new prime minister's first visit was to Scotland's first minister, Nicola Sturgeon. Theresa May has been forced to concede that she will not trigger article 50 until the devolved executives agree to a 'UK approach' for EU negotiations. If no satisfactory deal is done, the UK looks likely to disunite, leaving parliament sovereign over England and Wales alone.

Once Brexit negotiations begin, power will be in the hands of the EU institutions that enjoy final approval of any agreement, while the UK nervously watches the clock count down to the two-year deadline, at which point the country will be unceremoniously thrown out of the EU if no deal has been made, and relegated to deeply unfavourable World Trade Organisation terms.

Whatever deal is struck, will parliament want to rewrite so-called 'foreign' laws reflecting the globalised world in which we live? Brits get injured overseas: an EU Council directive provides for appropriate compensation. Flights are delayed, causing misery: again EU legislation provides a solution.

From fisheries to food poisoning and the environment to Erasmus, over the last 40 years we have implemented laws that recognise the need to collaborate with our neighbours to resolve problems which do not respect borders. The UK will continue to be affected by these factors; after leaving the EU we will have no influence in shaping its response. Parliament may, in the Diceyan phrase, be able to 'make or unmake any law whatever', but only within the UK. Britain can no longer influence EU law, yet EU law will still affect British interests.

The Vote Leave campaign failed to explain the distinction between sovereignty and influence, so carefully elided by the word 'control'. A sovereign parliament may have ultimate legal power, but little geopolitical influence. Throughout the 20th century the UK traded sovereignty for influence; by ceding power to international bodies such as NATO, the Council of Europe, the UN, and EU, the UK has retained influence in world politics. By 'taking control' the UK may have enhanced its sovereignty, but is set to lose much of its power.

Miranda Butler is a barrister at 3 Hare Court specialising in public law. From 2014 to 2015 she was the judicial assistant to Lord Kerr at the UK Supreme Court @mirandabutler3 @3harecourt