On 11 April, the European Council agreed to the Prime Minister's second request to extend the Article 50 period at the end of which the UK automatically leaves the EU. Under the 11 April European Council Decision, agreed by the UK, the new default date on which the UK will leave the EU is Thursday 31 October 2019, if Brexit takes place without a ratified Withdrawal Agreement in place.

If the Withdrawal Agreement were to be ratified on or before 31 October, the Agreement would come into force – and the UK would thus leave the EU – on the first day of the following month.

This includes the special situation that would arise if the UK were to ratify the Withdrawal Agreement on or before 22 May. In this case, assuming that the EU completed the procedures necessary on its side by 31 May, the UK would leave the EU on 1 June with a ratified Withdrawal Agreement in place, and without having had to hold the European Parliament (EP) elections due in late May. (This situation is provided for by recital 10 of the 11 April European Council Decision.)

This scenario – UK ratification by 22 May and exit on 1 June without having to hold EP elections – is being held out by the Prime Minister as her preferred option if possible. However, for the reasons we set out below, even on purely technical grounds it seems unlikely.

If the UK has not ratified the Withdrawal Agreement on or before 22 May, the UK must hold the EP elections, in its case on Thursday 23 May.

The UK was able speedily to put into place the critical legislative building blocks needed to accommodate the Brexit ‘flextension’, after the Prime Minister requested a further Brexit extension on 5 April and after the European Council agreed on 11 April. This was possible not least because uncertainty over – and the possibility of change to – the date of the UK’s withdrawal has been built into the statute book. Moreover, the nature of the delegated legislation involved meant that no action from Parliament was required:

• The legal foundation for implementing Brexit remains the EU (Withdrawal) Act 2018 (EU(W)A 2018). The Act plays this role most importantly because its Section 1 repeals the European Communities Act 1972 (ECA). However, ministers have not yet brought Section 1 into force (through a Commencement Order, which has no parliamentary scrutiny procedure). Ministers have indicated that they will do so only as one of the last steps before the UK exits the EU, and once the date of the UK’s withdrawal is certain and provided for in UK domestic law.

• Once all relevant commencements have been made, the repeal of the ECA – plus other repeals and a host of other changes across the UK statute book – will take effect on ‘exit day’. ‘Exit day’ is a UK domestic legal concept, established by the EU(W)A 2018, which functions as a trigger date for these multiple legislative changes. The EU(W)A 2018 defined ‘exit day’ as 29 March 2019. However, the Act also gave ministers a delegated power to amend this definition (via a Statutory Instrument – SI) so that it matches the date of the UK’s EU exit, should that date be changed from 29 March 2019. The EU (Withdrawal) Act 2019 (EU(W)A 2019 – the Cooper-Letwin Bill, as was) switched the parliamentary scrutiny procedure applicable to all future iterations of the SI amending ‘exit day’ from the affirmative to the negative procedure. Once the EU(W)A 2019 came into force on 8 April, this change of procedure allowed ‘exit day’ to be amended even more quickly than it had been the first time (before 29 March). A negative SI amending ‘exit day’ to 31 October 2019 was duly made on 11 April and came into force immediately.

• The legislative basis for the UK to hold European Parliament elections remains in place because the parts of the EU(W)A 2018 that repeal the relevant legislation have not yet been commenced. An SI made on 8 April under the still-effective European Parliamentary Elections Act 2002 set polling day as 23 May. This SI came into force on 10 April and was not subject to a parliamentary scrutiny procedure. If the UK were to ratify the Withdrawal Agreement by 22 May and thus need to cancel its EP election, some combination of Commencement Orders for the relevant repeals under the EU(W)A 2018, other SIs, and provisions in the EU (Withdrawal Agreement) Bill (WAB) could presumably be used to make any legislative changes needed to implement this.

The ratification requirements for the Withdrawal Agreement remain the same as they have been since passage of the EU(W)A 2018:

• on the UK side, under Section 13 of the EU(W)A 2018:

  • i) under Section 13(1)(b), approval of the Withdrawal Agreement and Political Declaration in a resolution of the House of Commons, on a motion moved by a minister (the so-called 'meaningful vote'), “so far as practicable” before the EP holds its consent vote;

  • ii) passage of the Withdrawal Agreement Bill (WAB) (under Section 13(1)(d)); and

  • iii) either fulfilment of the ratification requirements of the Constitutional Reform and Governance Act 2010, or the making of provision to exempt the Withdrawal Agreement from them.

• on the EU side, the consent of the EP, followed by the Agreement’s conclusion by the EU Council (under Article 50(2) of the Treaty on European Union).

The final step required in the Withdrawal Agreement’s ratification process is both sides’ notification of the Secretary-General of the EU Council (the Agreement’s designated depositary) that they have completed all their necessary internal procedures. It is the completion of this final step, by whichever is the later of the two sides, that will trigger the Withdrawal Agreement's coming-into-force on the first day of the following month.

On both the UK and EU sides, the political leaderships have, in purely technical terms, considerable scope over the timing and sequencing of the key steps in the ratification process.

Process questions for the UK government – including ones which will determine what Parliament will be asked to do and when – include:

• whether and when to hold another ‘meaningful vote’ for the purposes of ratification under the EU(W)A 2018 – the Act sets no deadlines for, or limits on the number of attempts at, the statutory approval motion(s);

• whether to move a single motion to approve the Withdrawal Agreement and Political Declaration together (as the government did on 15 January and 12 March) or possibly treat them separately (as it did on 29 March, with respect to the Withdrawal Agreement);

• whether to adhere to the longstanding government intention to introduce the WAB only after the House of Commons has approved the Withdrawal Agreement in the ‘meaningful vote’; or instead possibly reverse this sequencing, in order to demonstrate – or allow – the inclusion in the Bill of provisions increasing the prospects of Labour MPs shifting to pro-ratification positions;

• if the WAB were to be introduced only after approval of the Withdrawal Agreement in the ‘meaningful vote’, how long after the vote to introduce it (if there were a gap at all);

• how much time to try to programme in the House of Commons for the Bill’s consideration; and

• if and when the Withdrawal Agreement’s UK ratification conditions are met, when to take the final step of notifying the EU Council Secretary-General that the UK has completed its ratification procedures.

There might similarly be some discretion as to when the EU Council concludes the Withdrawal Agreement, and when the EU notifies the Council Secretary-General that its internal procedures are complete.

There should be no need for these steps to delay matters, however, since the EU Council has already approved a draft Decision to conclude the Withdrawal Agreement, amended to take account of the 11 April Brexit ‘flextension’.

On the EU side, the more pertinent questions about Brexit timings concern the EP.

The outgoing EP is now not scheduled to sit again. The new EP is not due to hold its constituent meeting until 2 July. After its second sitting on 15-18 July, and before the end of the extended Article 50 period, the new EP is then scheduled to sit again in September and October.

A Brexit with a ratified Withdrawal Agreement on 1 June or 1 July would therefore require the outgoing EP to be recalled for a special session in May or June to give its consent to the Agreement’s conclusion. (EP rules allow the EU Council, European Commission or a majority of MEPs to request that the Parliament be convened “on an exceptional basis”. One-third of MEPs are required for a quorum.)

The possibility of a recall was not discussed in the EP’s 16 April debate on the conclusions of the 10-11 April European Council, and a briefing note on the European Council meeting by the EP’s research service suggested that “the possible ratification of the Withdrawal Agreement would most probably only take place after the new European Parliament has started its activity.”

However, this may reflect assumptions on the EP side about the likely timing of any House of Commons approval of the Withdrawal Agreement.

If the House of Commons were to approve the Withdrawal Agreement, including if it did so earlier than expected, there would be significant political pressure on the EP to hold an extraordinary session to consent to the Agreement if necessary so that Brexit – with a deal – could take place as soon as possible. The unhappiness with the October extension expressed by some MEPs in their 16 April debate suggests that there could be support for such a move.

An EP spokesperson was reported as saying on 15 April that if the House of Commons approved the Withdrawal Agreement before 2 July there would be “the possibility, if necessary, of [the outgoing EP] having an extraordinary session”.

The Prime Minister's current plans are reportedly to reach agreement with the Labour Party on a set of terms that would allow that Party to support ratification of the Withdrawal Agreement, and then bring the Agreement back to the House of Commons for another ‘meaningful vote’ under the terms of the EU(W)A 2018.

With the current House of Commons having already declined twice to approve the Withdrawal Agreement and Political Declaration in the statutory ‘meaningful vote’ motion, as well as the Withdrawal Agreement separately in the third vote on 29 March, the most obvious procedural obstacle to this plan is the determination of the Commons Speaker to uphold the precedent that the House may not be asked to decide again on a question which is “the same, in substance” as one it has already decided during the same parliamentary session.

It would remain to be seen whether the fact that the Withdrawal Agreement has been amended, to accommodate new provisions on its date of entry into force, would enable the Speaker to allow another vote.

Publishing the WAB, and then referring to it in the 'meaningful vote' motion, might also be a way around the Speaker's position.

But the legislative timetable for the WAB would, in purely technical terms, still represent a significant obstacle to UK ratification of the Withdrawal Agreement by 22 May.

Going by the current parliamentary calendar, after its return from Easter recess on 23 April the House of Commons is due to sit for 17 days by 22 May, and the House of Lords for 16 after its return on 24 April.

On the basis of the official record, the amount of time that the government has thought necessary to pass the WAB has varied. The government first officially raised the prospect of requesting an Article 50 extension at the end of February, and on 14 March – after both the Withdrawal Agreement and 'no-deal' had again been rejected – it sought House of Commons approval for doing so. When the Withdrawal Agreement was rejected for a second time on 12 March, there had been just over a fortnight left before the original Brexit date (of 29 March) in which the government had, until then, putatively been aiming to pass the Bill.

However, in its 14 March House of Commons motion, the government sought approval for requesting an Article 50 extension to 30 June if the House approved the Withdrawal Agreement in the ‘meaningful vote’ by 20 March – a period of over three months in which to pass the Bill.

And in her 5 April letter to European Council President Donald Tusk requesting a further Article 50 extension, the Prime Minister again requested an end-date of 30 June, this time leaving a period of potentially somewhat less than three months in which to pass the Bill.

In effect, government policy on this issue has been driven by political considerations (such as the wish to leave the EU before the new EP convenes on 2 July), with the amount of time implied for passage of the WAB featuring as a side-effect.

Scrutiny of a Bill can be put on a fast-track timetable, and a number of creative solutions are available to facilitate accelerated handling of a Bill if required, although few of the options are likely to be popular with MPs and Peers.

For example, under the so-called No. 2 Bill process, two identical versions of the Bill could be introduced to allow simultaneous consideration in both Houses. This would avoid the delay which would occur if the Lords were to await the arrival of the Bill from the Commons and then observe the normal minimum intervals between each stage in the Lords. Under the No. 2 Bill procedure, the Bill would be introduced in the Commons, and shortly afterwards an identical Bill would be introduced in the House of Lords to which the words ‘No. 2’ would be added in the short title. The Bill would complete all its stages in the Commons and then be sent to the Lords. Before the Bill leaves the Commons, Bill No. 2 would receive its second reading in the Lords. When the Commons Bill was then received in the Lords, Bill No. 2 would be withdrawn, and the original Bill would proceed through its remaining Lords stages.

However, speedy passage of a Bill requires political agreement: in the House of Commons, to programme motions; and, in the House of Lords (in a situation more urgent than the No. 2 Bill process outlined above), potentially to setting aside Standing Order 46 which requires that different stages of a Bill be taken on different days. The Prime Minister’s 5 April letter to Donald Tusk implied that the programming of the WAB was among the issues on which the government was seeking agreement with Labour. But it is not clear that political agreement on a truncated scrutiny timetable would be forthcoming for the WAB, which will be a large, complex, constitutionally significant and politically highly sensitive piece of legislation. And this is especially the case given that ‘avoiding EP elections’ may not be seen as a sufficient justification for agreeing to the Bill’s speedy consideration.