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Following a vote in the referendum on 23 June 2016 in favour of the UK leaving the European Union, the Prime Minister said that this decision “must be accepted”, adding that “Parliament will clearly have a role in making sure that we find the best way forward”. Drawing on parliamentary material and recent legal and constitutional comment, this Library briefing examines what Parliament’s role would be in the process of withdrawing from the European Union in several key areas:

Invoking Article 50—The Prime Minister has said it would be for his successor and his or her Cabinet to decide whether the House of Commons should have a vote on the decision to trigger Article 50, the formal process set out in the Treaty on European Union for member states to follow should they decide to leave the EU. Some legal commentators agree that prerogative powers would enable a Prime Minister to take this decision; some have suggested that Parliament could have a role, and others have gone further, arguing that prior parliamentary approval would be required before Article 50 could be invoked.

Overseeing the Negotiation Process—Formal negotiations between the UK and the European Union would not begin until the UK made a notification under Article 50 of its decision to withdraw from the EU. Parliament’s involvement in overseeing or scrutinising such negotiations has not yet been set out in great detail. The chair of the House of Lords European Union Committee has called for Parliament to be “fully involved” in the process.

Ratifying Agreements—Parliament would have a statutory role in ratifying an eventual withdrawal agreement and any other international agreements arising from the negotiations if they were subject to the usual procedure for ratifying treaties. The House of Commons potentially has the power to block the ratification of a treaty indefinitely; the House of Lords does not. Under the terms of Article 50, the UK’s membership would cease two years after it gave formal notification of its intention to leave, if no withdrawal agreement had come into force by that point, although the two-year period could be extended on the unanimous agreement of all EU member states.

Repealing and Reviewing Domestic Legislation—As part of the process of leaving the EU, decisions would need to be made about how to deal with existing domestic legislation passed to enable EU law to have effect in the UK, a process which the House of Lords European Union Committee has described as “domestic disentanglement from EU law”. Parliament would have an important role to play in reviewing, repealing, amending and replacing legislation, a process which is predicted by many to be complex and time-consuming. Once the UK had formally triggered Article 50, its timescales would apply independently of Parliament approving domestic legislative changes associated with leaving the EU.


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