However, Parliamentary Sovereignty is still retained in some ways. Parliament doesn’t lose any sovereignty to intergovernmental institutions within the EU such as the European Council. Also, when unanimity is used within the Council of Ministers (on issues such as defence policy) the UK effectively has a veto and so no sovereignty is lost. Parliament agreed to submit to the precedence of EU law when it joined in 1973 and can also vote to leave the EU as well. In this way Parliament could be said to still retain ultimate sovereignty. Finally, this ‘loss’ of sovereignty could be viewed from another perspective; it has been argued that the UK ‘pools’ sovereignty in the EU, along with other member states, in order to actually gain more power. For example, by pooling sovereignty the EU can become stronger economically as it is in a more powerful position to negotiate trade agreements, e.g., when the EU forced the US to put down its steel tariffs by placing tariffs on US exports to the EU; the UK alone could not have achieved this, as it is too small.
Membership of the EU has also affected Constitutional Reform in the UK. Electoral reform has occurred due to the requirement of the European Parliament’s MEPs to be elected by a Proportional Representation (PR) system. In the UK we used a Closed List system. This introduction of a PR system has allowed British citizens to become familiar with PR voting and perhaps led the way for it to be introduced for other elections. Different sorts of PR are used for other elections in the UK, e.g., STV for the Northern Ireland Assembly. The voter could find this mix of different PR systems confusing however.
Devolution, introduced under New Labour, for Scotland and later Wales has been affected by the EU principle of subsidiarity where decision-making is taken at the lowest possible level. This has blurred the unitary nature of the UK constitution, devolving power to the UK regions. Parties such as the Scottish National Party (SNP) are very in favour of the policy of subsidiarity as it allows Scotland a greater measure of independence from the central control of Westminster.
The UK Constitution does not have an entrenched clause protecting Human Rights. The 1998 Human Rights Act includes the European Convention of Human Rights decided by the Council of Europe (a non-EU organisation) but this can be repealed at any time and UK policy can deviate from it if it is declared. However, if the new EU Constitution is ratified by all member states it will include a Charter of Fundamental Rights, however, these will only apply to EU law and therefore not all of UK law.
Finally, membership of the EU might encourage Parliamentary reform regarding the House of Lords (which has traditionally acted as a moderating factor on the government) as the EU encourages the ideal of liberal democracy. At present the House of Lords is not liberally democratic because it is unelected, and reform might be considered based on European examples such as the Bundesrat in Germany.
In conclusion, membership of the EU has certainly had big effects on the operation of the UK Constitution. However, in today’s globalised world, national sovereignty will never be complete as all countries now rely on global trade and investment and by transferring sovereignty to the EU it could be argued that the UK is controlling its power in the globalised world. As for the future implications of EU membership for the UK Constitution, if the EU Constitution is signed and the EU continues to expand more decisions will be made using QMV, signifying the shift of more sovereignty from Westminster to Brussels. The prospect of a federal Europe as envisaged by some would certainly have profound effects on the UK constitution, however, with 27 plus members in the future, a federal Europe would be huge and perhaps too big to agree to such a large change.