The impact of the EU on the fundamental principles of the UK constitution and Parliamentary Sovereignty 

How did membership of the EU change the UK?

EU Treaties became part of the UK's constitution

The process of making treaties is how the EU changes its structure and rules. There is no overall constitution so the treaties add up to the constitution of the EU. The treaties have allowed the EU to move to increasing integration with the development of the EU taking it from a primarily economic organisation to an increasingly political organisation. This process meant a steady transfer of elements of sovereignty from the UK  to the EU.

When the UK joined the EU it became subject to EU law. The Factor Tame Case established that EU law is supreme, however, EU laws are limited to specific areas and limited by the need to find agreement across the EU by unanimity or by qualified majority. The fact that the EU law applies in the UK has had a significant impact on policy areas such as environmental policy, health, and equality. It has also led to an unceasing sense that the UK has lost sovereignty.

EU membership enhanced devolution. Several policy areas in which the EU shares competence with the UK were devolved to Scotland, Wales, and Northern Ireland, including agriculture, fisheries, and the environment. On the subject of the UK's overall relationship with the EU, the central government had to consult the administrations in Edinburgh, Cardiff, and Belfast in order to produce an agreed negotiating position. This is why some writers described the UK as having a system of 'multi-level governance', in which policy-making is shared between the national government, the sub-national bodies in Scotland, Wales, and Northern Ireland, and the institutions of the EU. In this sense membership of the EU has cemented devolution into the working processes of the UK.

Individual rights and freedoms

The EU’s promotion of individual rights and freedoms across all member states has had mixed success. On the one hand, the principle of the freedom of movement has allowed citizens to move freely across borders in search of better and higher-paid jobs. Yet this in turn stoked tensions in countries such as the UK, which has seen high levels of immigration, especially from Eastern Europe. Fears over growing immigration numbers played an important part in the increasing support for Brexit.

Brexit has led to significant constitutional issues and revealed unresolved tensions within UK democracy. Faced with strong anti-Brexit sentiment within the Conservative Party, Boris Johnson expelled 21 pro-European Conservatives. Only four of them were reelected in the 2019 general election. As a result, the Conservative Party has shifted to become a fully Eurosceptic party, leaving pro-European Conservatives without a political home. 

It can be argued that Brexit has not strengthened parliament but has instead allowed the executive branch to increase its power. For instance, when Parliament refused to agree to an early general election in 2019, the Johnson government passed a law giving the prime minister the authority to set the election date. 

The Supreme Court clashed with the executive in two Gina Miller cases. In the first case in 2017, the court ruled that Parliament, not the executive, must decide to withdraw the UK from the EU. In the 2019 case, the court stated that the Johnson government could not suspend Parliament as it impeded its right to debate Brexit. These cases led to accusations that the Supreme Court was causing delays in Brexit and becoming too involved in politics.

Brexit damaged the United Kingdom's integrity. While 52% of voters supported leaving the EU in the 2016 referendum, the results varied among different parts of the UK. England and Wales had slight majorities for leaving, while Scotland and Northern Ireland voted decisively to remain. Scotland's pro-Europe stance has prompted the SNP to push for another independence vote with hopes of rejoining the EU. Following Brexit, the Northern Ireland Protocol was created to facilitate the movement of goods across the border with the Republic of Ireland, which remains in the EU. This has raised concerns among unionists in Northern Ireland about their UK membership. Consequently, the DUP exited power-sharing, causing the collapse of the Northern Ireland government in 2022. The disruption caused by Brexit to the UK constitution has led Labour to advocate for a significant shift in power to maintain the union. This would involve devolving power from Westminster and replacing the House of Lords with an elected Assembly of Regions and Nations.

Developments in devolution since Brexit

The feeling that the EU made laws without democratic oversight in the UK and based on the limited resources available to Parliament for scrutiny of EU regulations. Parliament did have a responsibility to examine EU legislation, and ministers should not have agreed to new laws unless it has been debated or reviewed by the House of Commons European Scrutiny Committee. In practice, however, the sheer volume of EU legislation makes this a difficult task to perform effectively. The House of Lords EU Select Committee produced thoughtful reports on developments in Brussels, but its status in the second chamber means that it lacks real influence. However, while this was seen by critics of the EU as more evidence of the insidious influence of the EU, the majority of EU regulations were not controversial ( to anyone but the Daily Mail) and are limited to uncontentious matters in to do with the environment or commerce. For example limits on the power of vacuum cleaners or the safe disposal of fridges.

EU membership  heightened the profile of the prime minister, whose annual routine has included attendance at regular European Council meetings. David Cameron visited his fellow heads of government individually early in 2016, as well as attending the Council, in a bid to renegotiate the terms of UK membership. Following the vote to leave the EU, Theresa May was thrust unexpectedly into the limelight as Britain's new prime minister, conducting a series of meetings with her counterparts in pursuit of a deal that protects vital national interests. British PMs are judged on their ability to stand up for the UK in Europe. Mrs Thatcher's status was enhanced by her success at achieving a rebate (return of money paid to the EU) and David Cameron lost status when he was seen to have failed to bring home significant concessions in the run-up to the referendum. (Cameron's EU deal)

Bexit failure undermined Theresa May. When Theresa May assumed office as prime minister in July 2016 after the unexpected EU referendum outcome, she garnered positive reactions from MPs and the public. Viewed as a reliable figure with vast experience from her time in the Home Office, May was widely seen as competent and accountable. Many believed she could navigate Brexit and advance the Conservative Party's objectives. However, her tenure came to an end in July 2019, influenced by Brexit and amid lingering divisions within her party and the country. What influence did Brexit have on her premiership and to what extent did it constrain her authority and accomplishments?

Boris Johnson used 'Get Brexit Done' to enhance his power. Johnson started with a minority government, facing challenges during Brexit negotiations. His failed prorogation attempt and clash with the Supreme Court in September 2019 preceded his successful call for a December 2019 election, supported by Parliament through a two-thirds majority. The UK exited the EU on January 31, 2020, marking the high water mark of Johnson's tenure as PM. The balance of power between parliament and the government changed when Johnson won an 80-seat majority at the 2019 general election. The executive is also strengthened by the extensive use of secondary legislation on Brexit policy because parliamentary scrutiny is limited here, as it is on international treaties.

As a member of the EEC/EU, the UK shared its sovereignty with other member states. The UK had to acknowledge the supremacy of European law over domestic law. The Factortame case (1991) established this principle in British law, requiring British courts to prioritize European law in cases of conflict. The question of whether parliamentary sovereignty had been compromised was resolved when Parliament initiated the process of leaving the EU in 2016, finalizing the withdrawal on 31 January 2020. This demonstrates that while the UK shared its sovereignty as an EEC/EU member, Parliament maintained the right to enact laws to fully restore parliamentary sovereignty, based on the principle that no parliament can limit its successor.

However, the outcome of the EU referendum led to conflicting assertions of sovereignty. Advocates of popular sovereignty cautioned against parliament obstructing Brexit, while proponents of parliamentary sovereignty contended that the referendum was not legally obligatory and that Brexit necessitated parliamentary approval. Brexit reinstates parliament's legislative power and diminishes the precedence of EU law, yet there are still practical constraints on the UK's capacity to assert political sovereignty while the use of referendums undermined the sovereignty of parliament. Parliament accepted the result of the EU referendum in 2016, although most MPs disagreed with it. This suggests that the political sovereignty of the public is superior to that of the Westminster Parliament.

The UK's departure from the European Union has restored full parliamentary sovereignty. The UK is no longer bound by the four freedoms of the EU, which include the free movement of goods, services, capital, and persons. The EU no longer has external sovereignty over the UK. This enables the UK to negotiate its trade agreements. However, existing EU laws have been incorporated into UK legislation through the EU Withdrawal Act.

It is also possible to argue that because of the cooperative relationships across the English Channel, the UK’s membership in the European Union has on balance enhanced rather than eroded effective U.K. autonomy. British skeptics can legitimately argue that the EU Commission and its governments may have adopted excessive regulations.  But skeptics cannot argue that those decisions were taken without U.K. participation.  Whatever future decisions may be made about Brexit, moreover, many of the existing cooperative relationships with the EU are likely to be maintained—precisely to forestall an unwanted deterioration in effective U.K. autonomy. 

However, Brexit has resulted in potential conflicts with EU member states over disputed territorial issues. For example, in 2021, the UK dispatched two warships to Jersey in response to French fishing boats threatening a blockade due to disagreements over post-Brexit fishing rights. The sovereignty of Gibraltar has also become a contentious issue, especially as the UK and Spain no longer share EU membership.

Effective U.K. autonomy depends more on the complex web of economic, social, and cultural interactions with the rest of the world than it does on the U.K. government’s formal political power.  

The EU–UK Trade and Cooperation Agreement was agreed on Christmas Eve 2020. Its key features were:

● There are no tariffs or quotas on goods traded between the UK and EU. But this is subject to rules of origin, meaning that goods (e.g. cars or food products) which include a high content of material produced outside the UK may face tariffs if exported to the EU.

● Non-tariff barriers, such as customs declarations and sanitary standards checks, are created.

● Tariffs can be imposed if the UK or EU believe that level playing field

provisions (e.g. on workers’ rights, environmental standards or state aid) have been breached.

● The UK’s share of fishing quotas increases by 25% for an initial five- year period. Annual negotiations on quotas will then commence.

● There is cooperation on law and security (e.g. data sharing and extraditions), but the measures are less robust than before Brexit.

● The UK participates in, and contributes to, some EU programmes (e.g. Horizon research funding) but will no longer participate in others (e.g. the Erasmus+ student exchange scheme).

● New institutional frameworks, including a partnership council, are created.

Brexit's Impact on Voting Behaviour

The 2017 and 2019 general elections were heavily influenced by Brexit. Similar to the 2016 referendum, voting behavior was influenced by the cosmopolitan versus non-cosmopolitan divide. Older, white, working-class individuals with limited educational qualifications and socially conservative views tended to favor the Conservative party, while younger, BAME, middle-class, and educated individuals with socially liberal views leaned towards Labour. Brexit allegiances often overshadowed party loyalties, with most voters aligning themselves with a party that shared their Brexit stance. Leave voters predominantly supported the Conservative party, while Remain supporters were more likely to back Labour.

Brexit and Political Parties

Divisions deepened within the two major parties following the EU referendum. May's Withdrawal Agreement faced defeat three times due to rebellions from Conservative MPs on both sides of the Brexit debate. Labour Remainers pushed for the party leadership to back a second referendum, while some Labour MPs representing Leave-voting constituencies advocated for a softer Brexit. After the 2019 general election, the Conservatives solidified their stance as a pro-Brexit party. Changes occurred within the party landscape as certain Labour and Conservative MPs switched sides to form Change UK in 2019, although the party disbanded in less than a year. The Brexit Party had a brief existence and later rebranded as Reform UK in January 2021. Support for UKIP dwindled after achieving its primary goal.