Brexit Stage Right - What Happens Legally If We Vote To Leave?

With only two weeks to the EU referendum, the latest ICM and YouGov polls show a 4 to 5 percentage point lead for the leave campaign.

Much can change in the days immediately before a referendum and - as we saw with the general election last year - polling can be far from a perfect indicator of how people will actually vote. That said, the result of the referendum is likely to be close.

Against this background, our public law experts examine the process for withdrawing from the EU, our options should we leave and the pace and degree of change to the UK's legal landscape following a Brexit.

The exit procedure

The starting point is that, should the UK vote to leave the EU, the process by which it does so will take a number of years, and in the meantime our legal landscape is likely to remain substantially unchanged.

The mechanism for exit lies in Article 50 of the Treaty on European Union. Under Article 50, if the UK decides to withdraw from the EU it must notify the European Council of its intention to do so. There will then follow a period during which the government and the European Council will negotiate a withdrawal agreement covering the terms of the UK's exit and its future relationship with the EU.

Despite David Cameron's assertion that a notice of withdrawal would be given immediately, this is unlikely in circumstances where the Chancellor has indicated that the government has not done a lot of thinking on what its negotiating position would be. In addition, many commentators consider it likely that there would be a change of Prime Minister and Cabinet following a vote to leave, which could add to the time before a notification is filed.

The UK would formally leave the EU - in the sense that the EU Treaties cease to apply to it - on the date on which the withdrawal agreement comes into force or two years after the date of its notification of withdrawal, whichever comes earlier. However, this period can be extended by unanimous decision of the Council in agreement with the UK government.

The negotiation process is likely to take at least two years due to the complexity of the issues in play and the range of interests to be considered. Indeed, the government's view is that the negotiations will take up to 10 years.

The leave campaign considers that to be a gross overestimate - during the Q&A session which we hosted at our Birmingham office on 1 June, Michael Gove indicated that he considers that the negotiations will take around four years. Evidence given to the House of Lords European Union Select Committee indicated that on the basis of negotiations for other trade deals between the EU and non-EU countries concluding the withdrawal agreement could take between four and nine years.

At the end of the negotiations the withdrawal agreement will need to be ratified by both sides, a process which - at least in the EU - is itself unlikely to be swift.

In the UK, the withdrawal agreement will be subject to the same process for ratification as any other international treaty. Under sections 20 and 24 of the Constitutional Reform and Governance Act 2010 the agreement would be laid before Parliament with an explanatory memorandum for 21 sitting days. During that time either House could resolve that it should not be ratified, but only the Commons could delay ratification indefinitely.

How smoothly that process went would depend on a range of political considerations. These would include the extent to which the government kept Parliament apprised and 'on side' during the negotiation process and whether the pro-EU majority of MPs wished to use their numbers to frustrate attempts by any anti-EU successor to the current government to establish a very limited form of ongoing relationship with the EU.

Once ratified, the withdrawal agreement would then be implemented by an Act, or Acts, of Parliament. Legislation would also be required to resolve the position in relation to existing domestic law which gives effect to EU law - the foremost example...