After a brief Easter pause the Brexit debate resumes today. Parliament returns from its Easter recess to face the unresolved problem of when and how the UK's exit from the European Union might take effect.

Immediately before MPs were sent home to rest and reflect, the government tabled the statutory instrument required to amend the definition of "exit day" in the EU (Withdrawal) Act 2018, section 20. Thanks to an amendment made by the Cooper-Letwin Bill, that instrument is subject to the negative procedure, meaning that it took effect immediately and would require a vote to strike it down, rather than requiring a positive vote to bring it into force. Consequently, the risk of a "no deal" Brexit on 12 April was averted.

The statutory instrument made only one change to the "exit day" definition, replacing 12 April with 11.00pm on 31 October 2019. While that time and date reflects the maximum period agreed by the EU Council on 11 April, it does not fully reflect the terms of the EU Council's decision.

31 October 2019 is the outer limit of the "flextension" agreed on 11 April. If the UK Parliament were to approve and ratify the Withdrawal Agreement before October, then Brexit would occur at the end of the month in which ratification took place. For example, if ratification occurred in May, then Brexit would occur, and the transitional period up to 31 December 2020 would begin, at the close of 31 May, with 1 June 2019 being "Brexit day".

It remains possible that the UK could leave with no deal. Recital (10) and Article 2 of the EU Council decision state that: "If the United Kingdom is still a Member State on 23-26 May 2019, and if it has not ratified the Withdrawal Agreement by 22 May 2019, it will be under an obligation to hold the elections to the European Parliament in accordance with Union law. In the event that those elections do not take place in the United Kingdom, the extension should cease on 31 May 2019".

In effect, failure or refusal to proceed with the European Parliament elections would result in the UK being ejected from the EU on a "no deal" basis.

The risk of a "no deal" Brexit would also recur if Parliament were unable to find a viable approach to the Withdrawal Agreement before the 31 October deadline. If little or no progress had been made by that point, there would be no guarantee of a further extension. The EU Commission is due to be replaced on 1 November 2019, with President Juncker stepping down at midnight on 31 October. The UK cannot be wholly confident that new leadership at the EU Commission, together with a newly constituted EU Parliament, would agree to a further extension – not least because the UK's participation in the EU Parliamentary elections disrupts the reallocation of seats agreed in view of Brexit. 31 October 2019 could, therefore, prove to be a hard deadline.

For business, as for Parliament, the problem remains essentially unchanged. The date on which Brexit might occur remains uncertain. The terms on which Brexit might occur remain uncertain. While the risk of a "no deal" Brexit has been reduced, it has not been eliminated. While the possibility of a "soft" Brexit, possibly involving some form of customs union, appeared to be gaining ground before the Easter recess, it is by no means certain that cross-party talks will arrive at an agreed outcome, or that a customs union on its own would resolve issues relating to the Northern Ireland border. Unless accompanied by continuing "regulatory alignment, a customs union would not remove the need for border checks. Consequently, while MPs might return refreshed from their Easter recess, the debate remains mired in familiar issues and disagreements.