UK: Constitutional Aspects Of Brexit

Last Updated: 27 July 2016
Article by Jonathan Haydn-Williams

Executive summary: The EU Referendum was advisory, not binding; no UK decision on 'Brexit' has yet been taken; although EU law has primacy, the UK has never given up sovereignty to the EU; the issue of whether Parliament has to legislate for a decision to leave the EU, before 'Article 50' notification is given, is the subject of English court proceedings; an alternative view is that the House of Commons should simply be consulted; any agreement between the UK and the EU as to 'Brexit' could be a treaty needing prior legislation by Parliament; alternatively, it could be subject to veto by the House of Commons; if not vetoed, Parliament would need to legislate to give it effect under UK law; in the absence of a withdrawal agreement between the UK and the EU, the UK will automatically drop out of the EU treaties two years after 'Article 50' notification, unless an extension of time is agreed.

The meaning of 'Brexit'

'Brexit' may mean 'Brexit' politically, but constitutionally its meaning is not so clear.

It is not a good start, perhaps, that the term itself is inaccurate in that the UK is not just 'Br'itain, but also includes Northern Ireland.

Gibraltar just squeezes on to the 'Brexit' label as a 'Br'itish Overseas Territory (the only such territory to be a member of the EU).

The Referendum Act and the result

At least the question on the ballot paper on 23 June 2016 was correct and in accordance with the European Union Referendum Act 2015 ("Referendum Act"), Section 1 of which required that:

"A referendum is to be held on whether the United Kingdom should remain a member of the European Union ... no later than 31 December 2017. ... The question that is to appear on the ballot papers is—

'Should the United Kingdom remain a member of the European Union or leave the European Union?' "

The Referendum Act made no provision for any action to follow the referendum, which was therefore advisory in nature and of no effect in law (but, of course, with extensive political effect). Referendums can be legislated for so as to be binding, such as the 2011 referendum (on whether to adopt the "AV" system of voting), but Parliament did not chose that approach for the EU referendum.

Presumably because of the referendum's non-binding nature, the Referendum Act did not state anything as to what type of majority was required. That is in contrast to the European Union Act 2011 ("EU Act 2011"), which made provision for a binding referendum of UK voters on any further transfer of power to the EU (including the creation of a common EU defence) and specified that approval had to be given by "the majority of those voting in the referendum", i.e. a simple majority of those who voted.

On the other hand, in the case of the binding 1979 Scottish referendum as to whether to create a devolved Scottish Assembly, Parliament provided for a threshold vote in favour by at least 40% of those entitled to vote. That was not reached and devolution did not proceed at that point. Such qualified majority voting is used in a number of other countries for decisions on constitutional change. The UK Parliament itself recently adopted it when including in the Trade Union Act 2016 provision for a strike of workers in 'important public services' to be illegal unless voted for by at least 40% of those entitled to vote.

The result of the EU referendum (as if you need reminding) was that 51.9% of those who voted were in favour of leaving the EU (representing 37.4% of those registered to vote). Politically, before and after the vote, the old and new Conservative governments took the position that the view of a simple majority of those who voted would be acted upon. Legally, however, no decision has yet been made as to leaving the EU.

UK Sovereignty: no repatriation needed (as it was never given up)

The issue of the ceding of sovereignty (meaning the Queen in Parliament) to 'Brussels', although a feature of the referendum campaign, had in fact been settled in 2011.

The European Communities Act 1972, passed by Parliament to give internal effect to the UK's accession to the Treaty of Rome (by which the UK joined the EEC, the predecessor of the EU), provided for EU (then EEC) law to form part of – and to have primacy over – the domestic law in the UK (i.e. that of England and Wales, Scotland and Northern Ireland). At that time, and later, there was controversy as to whether that statute was 'embedded' so as to deprive the UK Parliament of the right to repeal it, with the effect that UK sovereignty would have been transferred to the EEC/EU.

In order to settle that issue, the following declaratory provision was included as section 18 of the EU Act 2011:

"Status of EU law dependent on continuing statutory basis"

Directly applicable or directly effective EU law (that is, the rights, powers, liabilities, obligations, restrictions, remedies and procedures referred to in section 2(1) of the European Communities Act 1972) falls to be recognised and available in law in the United Kingdom only by virtue of that Act or where it is required to be recognised and available in law by virtue of any other Act".

The result, as concisely explained in Halsbury's Law's of England (5th edition), is that: "... in constitutional terms ... primacy of EU law does not mean that the authority of the United Kingdom Parliament is subordinate to it. The effect of EU law in the United Kingdom rests upon the ultimate authority of an Act of Parliament". Thus, constitutionally, 'Brexit' cannot include the repatriation of sovereignty to the UK because sovereignty was never ceded to 'Brussels'.

What will be needed in order to sever ties with EU law is the repeal by the UK Parliament of the 1972 Act, insofar as it gives legal effect and primacy to EU law within the UK.

Article 50 of the Lisbon Treaty

The EU 2007 Lisbon Treaty (further) amended the 1992 Treaty on the European Union ('Treaty of Maastricht') and the 1957 'Treaty of Rome'. Article 50 provides that:

"1. Any Member State may decide to withdraw from the [EU] in accordance with its own constitutional requirements".

"2. A Member State which decides to withdraw shall notify the European Council of its intention. ... the [EU] shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the [EU] ..."

"3. The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period".

Since the referendum, there has been disagreement about the effect of this Article, in particular whether the decision to withdraw from the EU is one for the UK government or Parliament or both. Clearly, actual notification will need to be made by the government, but does Parliament have to have any prior involvement? If so, of what nature?

The UK's "own constitutional requirements"

The government's position is that it is not necessary for Parliament to pass legislation in order for notification to be given to the EU under Article 50 para 2. That is being challenged in the English High Court, in the form of a judicial review application. A hearing is scheduled for 15 and 16 October 2016 and it is possible that it will reach the Supreme Court before the end of the year. The government has stated that it will not give the EU notification until early 2017.

As is well known, the UK does not have a written constitution. Instead, we have a number of constitutional conventions, the breach of which could lead to a so-called 'constitutional crisis'. They are therefore politically, rather than legally, binding and include that:

  • the Monarch will exercise her prerogative, executive powers in accordance with the advice from her Ministers;
  • Ministers are accountable to the House of Commons for the public acts of the Monarch (taken on their advice); and
  • although the supreme legislative power is the Queen in Parliament, she will not withhold her power of assent to any bill which has been passed by both Houses of Parliament (or just the House of Commons under the Parliament Acts).

The principle of ministerial accountability to the elected House of Commons is an important check on the use of executive power in the UK's democratic system. Had Parliament chosen to make the EU referendum binding, the House of Commons would have already had its say by – in effect – delegating the decision to the electorate. But since it chose to make the referendum, in law, merely advisory, one (perhaps persuasive) view is that it would be unconstitutional for the government to make a decision to withdraw from the EU and to act on it, without first consulting the House of Commons.

Consultation does not mean that Parliament would be asked to pass legislation to authorise the government to give Article 50 notification to the EU. Instead, the House of Commons could be asked to pass a non-binding motion to approve the government's intention. Given the scope available to the present, or a future, Parliament to 'put a spoke in the 'Brexit' wheel', the government might feel that the safe course is to obtain express backing of the Commons for 'Brexit', before changing circumstances make it politically less difficult for MPs to diverge from 'the will of the people'.

It has been suggested that if the government gave 'Article 50' notification without obtaining Parliamentary approval (whether in the form of legislation or a Commons motion), the notified decision would not fall within the scope of Article 50 para 1, in that it had not been taken "in accordance with [the UK's] own constitutional requirements". However, the EU surely cannot be expected, or be competent, to look behind a member state's notification of intention to withdraw, in order to decide whether that state's internal constitutional requirements have been met.

UK Treaties: entry, effect and withdrawal

Under the Vienna Convention on the Law of Treaties:

  • A 'treaty' is a written international agreement between different states, even if not called a treaty, which is governed by international law.
  • Withdrawal of a party from a treaty may take place in accordance with any provision for withdrawal contained in the treaty or by consent of all the parties to it after consultation between them.

Thus, withdrawal of the UK from the EU could take place either pursuant to Article 50 of the Lisbon Treaty or by separate agreement between all 28 member states. As set out above, Article 50 provides for a two year period in which to negotiate and conclude a withdrawal agreement and, at present, that seems to be the preferred route. It has the advantage or disadvantage (depending on one's view) that if an agreement cannot be concluded within that period and no extension of time is agreed, the EU treaties will cease automatically to apply to the UK, with no agreement having been made as to arrangements for UK withdrawal or the framework for the future relationship between the UK and the EU.

Under UK law, the term 'treaty' includes not only an agreement between states, but also one between states and international organisations. Thus, it seems that an agreement between the UK and the EU under Article 50 para 2 would amount to a 'treaty' under UK law.

Treaties are entered into on behalf of the UK by the Crown. Whilst the UK is thereby bound under international law, treaties are of no effect within the UK unless Parliament so decrees by passing a statute which has that effect.

For instance, when the UK joined the EEC (as it was then) by accession to the Treaty of Rome, it was necessary for Parliament to enact the European Communities Act 1972 so as to give domestic effect to that accession, which took effect on 1 January 1973.

It follows that if or when the UK and the EU conclude an agreement as to arrangements for the UK's withdrawal and for the framework of their future relationship, Parliament will need to pass legislation – at least to repeal the 1972 Act and related legislation and probably to introduce new laws to reflect the new relationship. Accordingly, the UK government in power at that time would need to be sure of Parliamentary support before entering into such an agreement. Indeed, in a 2011 note from the House of Commons Library, it was stated that: "UK practice is to try to make sure that new legislation is in place well before it ratifies [a] treaty".

Moreover, as explained in the next section, since 2010/2011 the scope of Parliamentary involvement in the approval of treaties has been extended by statute.

The CRaG Act 2010

The Constitutional Reform and Governance Act 2010 ("CRaG Act") requires that, save in 'exceptional cases', any treaty which requires ratification by the UK must first be laid before Parliament and published. Then, 21 sitting days must pass without either House of Parliament having resolved that the treaty should not be ratified. At that point the UK government may ratify the treaty so as to render it binding on the UK.

If the House of Commons resolves that the treaty should not be ratified, a Minister may present a statement as to why the treaty should be ratified. There is then a further 21 sitting day period in which the House of Commons may again resolve that it should not be ratified. If there is no such resolution, the treaty may be ratified. However, if there is such a resolution, the treaty may not be ratified.

'Ratification' is defined broadly, as acts of "deposit or delivery of an instrument of ratification, accession, approval or acceptance [or] deposit or delivery of a notification of completion of domestic procedures".

This measure gives the House of Commons the ability to block the entry into force of a treaty and thereby to defy the wish of the government of the day.

In the context of the UK's withdrawal from the EU, it means that a future Parliament could not only decline to give internal effect to a withdrawal treaty, but also (unless the government sought to declare it an exceptional case or somehow to skirt around the need for ratification) block the treaty coming into effect. In practice, this means that the government needs to work closely with Parliament throughout the process of withdrawal.

The CRaG Act procedure does not apply if Part 1 of the EU Act 2011 applies, which is considered in the next section.

Parliamentary approval under Part 1 of the EU Act 2011 of any treaty which amends or replaces the Treaty on European Union

As already mentioned, the EU Act 2011 provided for a binding referendum of UK voters on any further transfer of power to the EU. That provision now appears unlikely ever to be used. It featured surprisingly little in the pre-referendum debate.

However, Part 1 of the EU Act 2011 also provides that:

"A treaty which amends or replaces [the Treaty on European Union] ... is not to be ratified unless ... [it] is approved by Act of Parliament".

The writer has seen it suggested that this provision is, like the referendum provision, only applicable where a treaty involves further transfer of power to the EU, but he does not read the Act in that way. Not least, there is express provision for either "the referendum condition or the exemption condition [to be] met" (emphasis added). The "exemption condition" is "that the Act providing for the approval of the treaty states that the treaty does not fall within section 4", section 4 setting out the circumstances in which a referendum would be required. It follows that an Act of Parliament may be needed even where a referendum is not needed.

In the context of 'Brexit', a withdrawal agreement, under Article 50 para 2 of the Lisbon Treaty or otherwise, could – depending on its terms – be "A treaty which amends or replaces [the Treaty on European Union]" by virtue of the removal of the UK as a party and/or in other respects. If so, the UK government of the time would not be able to ratify it without Parliamentary approval in the form of a statute.

If the EU Act 2011 did not apply to the withdrawal agreement, the right of the House of Commons under the CRaG Act to prevent the ratification of the treaty (as explained above) would apply instead.


  • The EU referendum was advisory, as Parliament chose not to make it binding (unlike the binding 2011 referendum on 'AV' voting).
  • No provision was made as to any type of required majority. Previous binding referendums have opted for a simple majority of those who voted or a 40% minimum threshold of those entitled to vote.
  • No legally binding UK decision on 'Brexit' has yet been taken.
  • Since 1972/3, EU law has had primacy over UK law. However, the UK has never given up sovereignty to the EU: a declaration to make that clear was included in the EU Act 2011.
  • The issue of whether Parliamentary legislation must be passed before the government can give 'Article 50' notification to the EU of a decision to leave is the subject of English court proceedings, which may conclude before the end of 2016.
  • An alternative view is that the House of Commons should be consulted, by means of a motion, as to whether notification should be given.
  • The 'Article 50' route means that if an agreement as to arrangements for the UK's withdrawal were not concluded within two years of notification (or such longer period as might be agreed), the EU treaties would automatically cease to apply to the UK, without any arrangements being put in place for the withdrawal or as to the future relationship between the UK and the EU.
  • Under international law, the alternative to the 'Article 50' route would be for all 28 member states to consult and, if possible, reach an agreement as to the UK's withdrawal.
  • An agreement between the UK and the EU as to arrangements for 'Brexit' could amount to a treaty needing legislative approval by Parliament under the EU Act 2011.
  • Alternatively, ratification of that treaty would be subject to veto by the House of Commons under the CRaG Act 2010.
  • Parliament would need to pass legislation to give effect within the UK to any 'Brexit' agreement between the UK and the EU.
  • The UK government and UK Parliament will need to work together in relation to 'Brexit'. Parliament's role is far from a 'rubber stamping' exercise. Indeed, it has the power to block any withdrawal agreement. In that respect, it has to be borne in mind that the present government and Parliament may not still be in place when the time comes to conclude such an agreement.

This article was written by Jonathan Haydn-Williams, Senior Counsel, Dispute Resolution, assisted by helpful suggestions from Stephen Hornsby, Partner, Dispute Resolution.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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