The Mechanics of a Further Referendum on Brexit Revisited: Questions for the New Parliament

A further referendum on Brexit is central to many parties’ general election pledges. Today, the Constitution Unit launches a new report examining how such a vote might come about and what form it might take. This updates previous work conducted last year. In this post, adapted from the report’s final chapter, Alan Renwick, Meg Russell, Lisa James and Jess Sargeant sum up the key conclusions. They find that, though it would not be without difficulties, a vote on Johnson’s deal may be the quickest option and the one most likely to command public legitimacy. 

The Constitution Unit’s latest report, The Mechanics of a Further Referendum on Brexit Revisited: Questions for the New Parliament, is published today. It significantly updates our previous analysis of the mechanics of a further Brexit referendum, exploring the circumstances that might lead to a further referendum on Brexit, and the form that such a referendum might take. The report does not advocate for or against a referendum, or assess the broader impact that such a vote might have. Rather, it explores the practical implications of the different options: in terms of the processes to bring a referendum about, the standards that it should meet, the options for reforming regulation, and, crucially, the timetable.

The minimum timetable from the point at which parliament decides in principle to hold a referendum to the date on which that referendum is held is roughly 22 weeks – or five months. Claims that organising a referendum would take a year or more are therefore overstated. However, very clearly, a decision to proceed with a referendum would require a further extension to the Article 50 period, which currently expires on 31 January 2020. And there are various factors that could put pressure on the minimum timetable, requiring a somewhat longer period of planning and preparation. This post (adapted from the report’s final chapter) considers how the pieces fit together, and what the overall timetable would likely be. The most obvious implication of this is for the length of Article 50 extension which a future government should request if seeking to hold a referendum.

The report considers the factors which could impinge on the timetable in detail, but in brief they include the following:

  • Is the referendum to be held on a pre-existing Brexit deal, or is time required (as Labour’s policy implies) for further renegotiation before proceeding to a referendum?
  • How contentious would the referendum bill be in parliament? This depends partly on the constellation of parties and groups in the House of Commons after the general election, and also on the content of the bill.
  • What form would the referendum question take? This may be one of the points of contention in parliament. We conclude that a three-option referendum is unlikely. Moving to such a format would slow down the process.
  • To what extent would campaign regulation be tightened up and updated via the referendum bill? Some updating is essential, and could be incorporated within the 22-week timetable. Other more major changes might be desirable, but in the interests of speed would likely be set aside.
  • Would the referendum result be made legally binding? This is not essential, but would be beneficial to provide clarity and certainty for voters. Preparing for a fully legally binding referendum would be likely to take slightly more time.

The effect of these factors is summarised in the figure below, in simplified form. This assumes a simple binary referendum question, rather than building in the unlikely possibility of a three-option poll. It allows for slow and fast timetables for Labour’s renegotiation with the EU27 – respectively allowing three months for this process (as proposed in the party’s own timetable) or just one month (to allow Labour to meet its promise of holding a referendum within six months). A six-month timetable could not accommodate other delays, which might arise, for example, if some of the changes to the regulatory framework proved particularly controversial, or if making the referendum result binding proved difficult. If the timetable restriction were relaxed, these changes could be more easily fitted in.

Possible routes to a referendum


The quickest route to a referendum would clearly be to proceed immediately after the election to a binary vote on Boris Johnson’s deal versus Remain. The scenario most likely to bring this about is a minority Conservative government dependent on support from pro-referendum forces in the House of Commons (potentially, any other group except the Brexit Party). In this case, the passage of the European Union (Withdrawal Agreement) Bill could be made conditional on the approval of the deal in a referendum. The bill already exists, and was introduced into the House of Commons shortly before the general election. It could therefore be quickly reintroduced. An assurance from the Prime Minister that a referendum amendment would be accepted could secure the bill’s second reading, and see it proceed to committee stage where such an amendment could be introduced. If approved in principle, provisions to allow for the referendum could then be included within the bill. This would result in a referendum that was binding in the event of a Leave vote, as the bill to implement the outcome would already be on the statute book. Referendum supporters would no doubt want to ensure that it was also binding in the event of a vote for Remain, by including provisions requiring the Prime Minister to revoke Article 50 and repeal existing Brexit legislation. If the Commons majority for this compromise solution held together, a referendum might be held in late May or June 2020 – assuming that the regulatory changes were limited to the essentials. In terms of regulation, Remain-supporting MPs would clearly wish to ensure some tightening up, particularly regarding the government’s role in the referendum campaign and the extent to which it could use its resources to encourage a Leave vote.

There could – perhaps counterintuitively – be some attractions for a Labour-led government in pursuing a similar course. Given that Johnson’s deal already exists, this would expedite the referendum timetable. In addition, it would maximise the legitimacy of the referendum among Brexit supporters, who would likely consider a Labour deal (which envisages a closer future relationship with the EU) as not offering a ‘real Brexit’. However, importantly, a Labour government would need to be prepared to implement Johnson’s deal in the case of a Leave vote. Labour’s own concerns, alongside those of the Northern Irish unionist parties and others about the deal’s potential impact on the Union, would be a significant obstacle. If this route were to be chosen, one key difference to the scenario under a Conservative-led government is that a parliamentary coalition in favour of a referendum might prefer to set aside the EU (Withdrawal Agreement) Bill and move straight to an in-principle referendum on the deal versus Remain. This could speed matters up slightly, given the delays that are possible during the passage of that bill. However, it would likely attract criticism from Brexit supporters, who would prefer the certainty that a Leave outcome in a further referendum would be legally binding and have immediate effect. From the point of view of legitimacy, therefore, it could still be beneficial for the parliamentary majority to demonstrate its commitment to respecting the outcome by passing the EU (Withdrawal Agreement) Bill on a conditional basis. 

Labour’s proposed timetable of renegotiating the deal and holding a referendum within six months is challenging. It would be difficult in practice to test and finalise the referendum question unless the deal had already been secured. This would hence slow down the party’s proposed six-month referendum timetable, unless a new deal was secured very quickly indeed. Making that deal binding in the event of a Leave vote, through passing a full Withdrawal Agreement and Referendum Bill, as the party proposes, would be wise; but it would add to the timetabling challenges. The alternative of a non-binding referendum on an agreement that included a perhaps necessarily vague Political Declaration (given the haste of the negotiations) could meanwhile be problematic in terms of the clarity and certainty of the Leave outcome. It would add to the pre-existing concerns among Brexit supporters, who would both oppose a referendum in principle and likely consider this an unacceptable deal. If this kind of dissatisfaction led Brexit supporters to boycott the referendum it would raise very serious concerns about the legitimacy of the outcome, which could have long-lasting negative effects.

Allowing more time for Labour’s renegotiation would stretch the timetable beyond the party’s preferred six months, requiring a minimum of closer to eight months. This would imply a referendum in the autumn of 2020. If a longer timetable were allowed, this could provide space for more careful consideration of the reforms necessary to campaign regulation, perhaps with some consultation on these matters taking place alongside the negotiations with the EU. Clearly this could have advantages; however, these would be counterbalanced by the inevitable frustrations and uncertainties that would be created by further delay.

In general, as pointed out by the Constitution Unit’s Independent Commission on Referendums, the UK could greatly improve how it uses this form of public participation – in terms of campaign regulation, but also improving opportunities for informed discourse, and building other participation mechanisms into the process. Referendums can usefully involve citizens in setting the question, deliberating on the options, and producing trustworthy briefing materials for other citizens in making their choice. Scope for using mechanisms such as citizens’ assemblies for a further Brexit referendum is more limited than it would have been before the poll held in 2016. Nevertheless, some measures of this kind – such as a broadcaster-led citizens’ panel examining the implications of each of the options on the ballot paper – could, and ideally should, be included. They would be feasible within six months, while extending the referendum timetable to around eight months would allow such options to be developed more fully.


A further referendum on Brexit is most likely to come about if a Labour-led government forms after the coming election, though it could also happen if a weak Conservative government were forced to accept such an outcome by pro-referendum parties. Holding a referendum would take a minimum of 22 weeks, or five months. Keeping to that timetable would be easiest – and the legitimacy of the vote would likely be highest – if the referendum offered a straight choice between leaving the EU on the terms of Boris Johnson’s deal or remaining in the EU. This would allow such a referendum to take place in May or June 2020. If a Labour-led government sought to renegotiate the deal first, by contrast, the six-month timetable that the party proposes may well prove challenging. A slightly longer timetable would, however, make it easier to address the most egregious failings in current referendum campaign regulations, and take steps to improve the quality of campaign discourse. It would also be easier to make the result of the vote legally binding under a slightly longer process. Even taking this into account, a referendum, if parliament wanted to pursue such a route and there was a House of Commons majority to deliver it, should be possible by September 2020.

Whatever the parliamentary arithmetic, any further referendum is likely to remain publicly contentious. If one is to be held, it is imperative that it should enjoy maximum legitimacy and thus that it should be conducted well.

The Mechanics of a Further Referendum on Brexit Revisited: Questions for the New Parliament, by Alan Renwick, Meg Russell, Lisa James and Jess Sargeant was published today by the Constitution Unit, jointly with the UK in a Changing Europe. It is downloadable from this link.

If you enjoy the Constitution Unit blog, sign up for updates in the left sidebar, join our mailing list for news of our events and research, and support us through a one-off or regular donation. Donations are crucial to funding the blog, and the Unit’s research.

About the authors

Alan Renwick is Deputy Director of the Constitution Unit.

Meg Russell is Director of the Constitution Unit.

Lisa James is a Research Assistant at the Constitution Unit, working on the ‘Brexit, Parliament and the Constitution’ project.

Jess Sargeant was a Research Assistant at the Constitution Unit from July 2017 to September 2018.