The Prime Minister has now officially requested an extension of the Brexit deadline to 30 June 2019 to enable her to bring the negotiated withdrawal deal (the legally binding Withdrawal Agreement and the Political Declaration on future relations) back to Parliament for a third 'Meaningful Vote'. The President of the European Council, Donald Tusk, responded that a short extension would be possible, but would be conditional on a positive vote on the withdrawal deal.

Assuming that an extension to 30 June 2019 (or whatever alternative date the EU agrees to) is agreed, what will need to happen for the UK to actually exit the EU? If the House of Commons approves the withdrawal deal in 'Meaningful Vote 3.0' there will be a series of further stages of approval and ratification at the UK and EU level before Brexit becomes official.

1. Amending "exit day" under UK law

In the immediate short term, assuming that an extension is agreed, there will need to be a swift amendment of the EU Withdrawal Act 2018 ("EWA"). At present Section 20(1) of the EWA defines "exit day" as 29 March 2019 at 11.00 pm GMT. At that point there will be a series of changes under the UK law, including the repeal of the European Communities Act 1972. If there is an extension of the Article 50 deadline, the definition of "exit day" will need to be amended prior to 11.00pm GMT on 29 March 2019 so as to avoid these changes taking place.

Section 20(4) EWA provides that amending "exit day" can be completed by statutory instrument ("SI") under the affirmative procedure. The affirmative procedure means that the relevant SI must be actively approved by both Houses of Parliament. An SI under the affirmative procedure will be debated in either a delegated committee or on the floor of the House. While the draft affirmative procedure is not subject to any particular deadline, it will need to be accelerated to ensure that the SI is completed before 29 March.

2. Meaningful Vote 3.0

The Prime Minister has confirmed her intention to bring the negotiated withdrawal deal back to the House of Commons for a third 'Meaningful Vote' as soon as possible. The plan to do so this week was scuppered by the Speaker of the House of Commons confirming on 18 March that under parliamentary rules in order for a further meaningful vote to be brought back to the House of Commons, the agreement would have to be "fundamentally different – not different in terms of wording, but different in terms of substance". At present it is unclear how the Government will respond. It is possible that an agreed extension to Article 50 could be sufficient to persuade the Speaker not to block 'Meaningful Vote 3.0'. The Speaker is likely to have to show some flexibility given that the rule he is relying on from Erskine May (the most authoritative work on parliamentary procedure and the constitutional conventions regarding the UK Parliament) applies to amendments just as much as to motions – and would therefore theoretically rule out further votes on all other options as well (eg on a second referendum, the UK proposing to join the EEA and so on).

In any event, if a majority in the House of Commons is in favour of a third 'Meaningful Vote', the vote is likely to happen as MPs could vote to suspend or change the "standing orders" of Parliament in order to bring the motion to a vote.

If the House of Commons approves the withdrawal deal, section 13(1)(c) of the EWA allows the House of Lords the opportunity to debate the deal for a period of up to five Lords sitting days beginning on the date that the House of Commons passes the resolution approving the deal. The House of Lords will not actually have a vote on the withdrawal deal.

See here for further information on how the 'Meaningful Vote' works.

3. Enshrining the deal in a UK statute

If the UK Parliament approves the withdrawal deal Section 13(1)(d) of the EWA requires there to be an Act of Parliament (the "EU Withdrawal Agreement Bill" or "EWAB") which contains provisions for implementation of the Withdrawal Agreement into UK law. This will include provisions which stipulate a legal basis for the transition period; ensure citizen's rights; provide for payment of monies to the EU; and defer most EU exit SIs made under the EWA and otherwise.

The EWAB is a constitutionally significant bill and therefore MPs will want time to debate it. Past bills to implement major EU treaties have taken between 10 and 40 sitting days to get through Parliament. More controversial treaties have tended to take longer. Unlike the approval motion for the withdrawal deal, the House of Lords will have a vote on the EWAB.

For further details on the EWAB see question 6 in the Withdrawal Agreement Q&A section of our Brexit Legal Guide.

4. Ratification in the UK

As the Withdrawal Agreement (but not the Political Declaration) is a treaty it must be laid before Parliament under the Constitutional Reform and Governance Act 2010 ("CRAG"). Section 20 of the CRAG allows Parliament 21 sitting days to vote against ratification of a treaty. If Parliament votes against the treaty, a Minister may lay before Parliament a statement that the treaty should nevertheless be ratified and will need to explain why. The House of Commons (but not the House of Lords) is then permitted a further 21 days to vote against ratification of the treaty. This means that, in theory, the Withdrawal Agreement could be blocked indefinitely by the House of Commons repeatedly passing motions to the effect that the treaty should not be ratified.

The requirements of the CRAG could be avoided if the Government includes a provision in the EWAB to say that its passage fulfils the requirements of the CRAG. Alternatively, section 22 of the CRAG enables the procedure to be avoided if a minister believes there is an exceptional case. There is no indication in the CRAG of what might constitute an exceptional case – the Government is free to designate anything as exceptional. The Government has not indicated that it intends to legislate to bypass the requirements of CRAG or designate this treaty an exceptional case.

5. Ratification in the EU

Article 50 (TEU) requires the European Council to agree the Withdrawal Agreement, acting by qualified majority (see below), after first having obtained the consent of the European Parliament. For the avoidance of doubt, the Council of the EU is not the same as the European Council. The European Council consists of the heads of the Member States and defines the overall political direction of the EU, including setting EU's mandate on the Brexit negotiations. The Council of the EU is one of the two legislative bodies in the EU (the other being the European Parliament), consisting of a minister from the relevant policy area from each Member State.

Once the UK Parliament ratifies the Withdrawal Agreement, the Council of the EU will submit it for approval by the European Parliament. The European Parliament needs to give its consent in a simple majority vote of members present. This will include MEPs from the UK. Given that the Withdrawal Agreement concerns a Member State's withdrawal from the EU, it falls within the category of special legislative procedures and as such ratification is completed via the consent procedure. Under this procedure, the European Parliament does not have the power to propose amendments to the Withdrawal Agreement.

Given the upcoming elections on 23 to 26 May 2019, the final sitting of the currently constituted European Parliament is scheduled for 18 April 2019. If the Withdrawal Agreement is not ready for ratification by that date however, according to the Rules of the Procedure of the European Parliament, it is still possible to recall the outgoing European Parliament until the first sitting of the new Parliament on 2 July 2019. This should ensure that it is still possible to consent to the Withdrawal Agreement after 18 April.

The Council of the EU (excluding the UK) then needs to approve the Withdrawal Agreement by a super qualified majority vote. A "super qualified majority" is defined as at least 72% of the members of the Council representing Member States comprising at least 65% of the population of the EU. This means at least 20 Member States will need to approve the Withdrawal Agreement.

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.