For most of the Brexit process so far, Parliament (and others affected) had to work to only one date on which Brexit would occur, with or without a deal: 29 March 2019.

Then, for a week between the European Council meeting of 21 March (which granted the first Article 50 extension) and the House of Commons’ third rejection of the Withdrawal Agreement on the cut-off day of 29 March, there were officially two possible Brexit dates: 12 April for Brexit-without-a-deal, and 22 May for Brexit-with-a-deal.

Between the House of Commons’ 29 March rejection of the Withdrawal Agreement and the European Council's 11 April Decision to grant a further Article 50 extension, officially only one Brexit date survived (12 April).

But since the 11 April European Council Decision, agreed by the UK, the UK could in principle leave the EU on multiple dates: without a ratified Withdrawal Agreement on 31 October, or with a ratified Withdrawal Agreement on any one of six dates – the first of June, July, August, September, October or November. (It is too late for the theoretical possibility, under the European Council Decision, of 1 May.)

This multiplication of possible dates for Brexit arises because the European Council Decision in effect makes the date of Brexit-with-a-deal into a conditions-based one, rather than one fixed in advance. This switch in the nature of Brexit-with-a-deal coexists with the previous, fixed-date, nature of Brexit-without-a-deal.

For Parliament, the multiplication of possible Brexit dates matters because leaving the EU will bring a host of changes to parliamentary responsibilities, practices and inter-institutional relationships.

Purely for planning purposes, it would be helpful to know the date on which these changes will need to be in place. The potential dates now span a period of six months, from June to November.

Most importantly (given that the multiplication of possible Brexit dates applies to Brexit-with-a-deal, not Brexit without), if the Withdrawal Agreement enters into force it will – as we set out a year ago – require Parliament to have arrangements in place in order to engage with its provisions. These arrangements will need, at a minimum, to allow Parliament to deal with new EU law coming into force during the post-Brexit transition period, and to scrutinise the UK side of the UK-EU Joint Committee and its sub-committees. Parliament will also need to be ready to play the greater role that the government has promised, and that many parliamentarians seek, in the UK’s negotiations with the EU on the post-transition relationship.

It is unclear whether the Withdrawal Agreement Bill (WAB) – needed to implement and allow ratification of the Withdrawal Agreement – will be the major vehicle for such parliamentary arrangements to be put into place. Ideally, procedural matters should not be provided for in legislation. However, given the lack of trust in the government that by now prevails among many MPs, they may insist that provisions for parliamentary scrutiny be put on a statutory footing. Whether they are provided for by legislation, changes to Standing Orders or other means, provisions for parliamentary scrutiny under the Withdrawal Agreement will need detailed consideration.

Even if the UK were to leave the EU without a Withdrawal Agreement, however, scrutiny questions would arise. To give two important examples:

• The UK will regain the legal competence to negotiate its own trade agreements as soon as it leaves the EU (but, with the Withdrawal Agreement in place, without EU authorisation will not be able to bring them into force during the post-Brexit transition period for which the Agreement provides). Parliament needs to be ready to scrutinise the negotiation of such agreements as soon as the UK leaves.

• After the UK leaves the EU, the Prime Minister will no longer be a member of the European Council and therefore no longer required by convention to make oral statements to the House of Commons after European Council meetings. Whenever this takes place, it will free up some time on the floor of the House, but reduce the number of the Prime Minister’s appearances there. What alternative arrangements, if any, will be put in place to hold the Prime Minister to account for post-Brexit EU-related policy-making, beyond her appearances at Prime Minister's Questions and three times a year before the Liaison Committee? And what might be done with any extra time freed up on the floor of the House?

The Brexit ‘flextension’ requires action during a period – Easter-to-October – which, for Parliament, is usually a disrupted one. After recesses were cancelled in February and cut short at Easter, this raises the possibility that future recess periods in 2019 may be affected.

For Parliament, in a non-general election year, the period between Easter and October would normally see:

• a Whitsun recess, of, in effect, a calendar week in late May/early June;

• a Prorogation of at least a few days, ahead of State Opening in May or June;

• after State Opening, debates in both Houses on the Queen’s Speech which are the main item of business usually for five sitting days;

• a summer recess of around six weeks; and

• a three-week conference recess in September-October.

In just over six calendar months between November and early May, in both 2016-2017 and 2017-2018 there were 89 House of Commons sitting days. By contrast, in the same amount of calendar time but between 23 April and 31 October, in the last two non-general election years (2016 and 2018) there were 64 and 70 House of Commons sitting days, respectively.

If there are no changes to the normal parliamentary schedule in the months ahead, this could cause difficulties for the Withdrawal Agreement Bill, if that is not passed speedily in May to meet the deadline to avoid holding EP elections. If the government's current negotiations with the Labour Party were to fail to produce agreement on a package allowing ratification of the Withdrawal Agreement, and the government were to embark on a further set of House of Commons indicative votes, this would take up further time on the floor of the House. However, the disrupted parliamentary timetable could be especially problematic if there were an effort to legislate for a no-deal Brexit before 31 October.

Five Bills which the government has indicated would be needed for a legislatively sound ‘no-deal’ Brexit remain to be passed. The Trade Bill awaits only 'ping-pong'; and the Financial Services (Implementation of Legislation) Bill, which started in the Lords, has completed its stages there and awaits report stage in the Commons. However, the Immigration and Social Security Co-ordination (EU Withdrawal) Bill, the Agriculture Bill and the Fisheries Bill are all at the same, pre-report, stage in the Commons without having started their passage in the Lords.

Not proroguing Parliament in May or June, and thereby avoiding the Queen’s Speech debates, would create some extra legislative time. (For the government, given its lack of a House of Commons majority, this might also be politically expedient.)

There is no requirement that a Prorogation and State Opening take place every year, and no limit on the length of a parliamentary session. Asked in the House of Commons on 11 April about the timing of the end of the parliamentary session, the Prime Minister merely reiterated her focus on getting the Withdrawal Agreement approved.

However, in addition to the possibilities suggested in our companion blogpost, proroguing Parliament and starting a new session would be one way around the potential obstacle to the Withdrawal Agreement’s ratification represented by the determination of the House of 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.

(In terms of the number of House of Commons sitting days, by far the longest parliamentary session since 1945 was that of 2010-12, with 295. On the basis of the current sitting schedule, the House of Commons’ 2017-19 session is set to equal this on 2 May. Whenever Prorogation occurs, the 2017-2019 session is thus set to be the longest since World War Two.)

The current House of Commons Speaker, John Bercow, was elected in 2009 and has already remained in post past his initial pledge to step down in mid-2018.

In the run-up to the 2017 general election, Mr Bercow indicated that he would wish to serve the full Parliament if re-elected as Speaker.

However, after publication of the critical Cox report on the culture of the House of Commons, it was reported in October 2018 that he was planning to step down in summer 2019.

The first signs of a Speakership election race are now evident. Possible contenders are believed to include the current Deputy Speakers, Lindsay Hoyle and Dame Eleanor Laing, and Labour MPs Chris Bryant and Harriet Harman.

However, although the Speaker has not explicitly linked his fate with that of Brexit, it has also been reported that he would like to see the Brexit process through.

In this case, the Brexit ‘flextension’ could delay Mr Bercow’s resignation and the election of a new Speaker. However, given the hostility among some MPs to Mr Bercow's continued Speakership (not least because of some of his Brexit-related decisions), it could also conceivably help to prompt an attempt by MPs to remove him against his wishes. The influential Conservative backbencher Crispin Blunt MP is already rumoured to be canvassing support for a motion of no-confidence in the Chair.

Under the April 'flextension', a 'no-deal' Brexit on 31 October remains the legal default. MPs might therefore again take action to seek to avoid this.

(The 11 April European Council Decision left a second mechanism by which the UK could, in principle, leave the EU with no deal, namely automatic exit on 31 May if the UK has neither ratified the Withdrawal Agreement by 22 May nor held its European Parliament elections on time. However, this appears legally and politically impossible.)

The Prime Minister’s policy choices of recent weeks, and the 11 April European Council Decision to grant an Article 50 extension, appear to indicate that neither side wants a no-deal Brexit.

The current House of Commons has demonstrated a repeated majority against a no-deal Brexit, and in extremis it could block the government’s conduct of business in order to try to obstruct any prospect of this outcome.

However, it is not certain that the EU would grant a further extension beyond 31 October; and the Prime Minister’s policy of avoiding a no-deal Brexit remains a matter of politics, not law.

The previous House of Commons rejected a Lords amendment to the EU (Notification of Withdrawal) Bill in March 2017 that would have required parliamentary approval for a no-deal outcome; and, in order to avoid a no-deal Brexit, the recent EU (Withdrawal) Act 2019 (the Cooper-Letwin Bill, as was) required the government to seek the House's approval for an Article 50 extension only on the day on which the Act received Royal Assent (i.e. 8 April 2019) or on the day after that day.

It is therefore possible that the Brexit extension to 31 October might require parliamentarians opposed to a no-deal Brexit to again take steps to avoid one. This raises the prospect of possible further attempts by backbenchers to take control of the Order Paper.