UCL News


A Brexit referendum is possible, but contingency planning must start now

9 October 2018

A referendum on Brexit is clearly possible, but the details matter. Various processes must be put in place to ensure the referendum is legitimate, according to a new report by the UCL Constitution Unit.

Brexit referendum demonstration

The report titled 'The Mechanics of a Further Referendum on Brexit' highlights the constitutional and legal questions that must be considered, including: the timeline, how a referendum could be triggered, the format of the question, and what rules should govern its operation. Key conclusions include:

  • A new referendum requires legislation: ensuring proper scrutiny of this, and adequate preparation for the poll would take at least 22 weeks.
  • This would demand an extension to the Article 50 period, which should be achievable - but does open up some complications, particularly regarding the European Parliament elections due in May 2019.
  • There are various trigger points for a referendum. Parliament could demand a referendum in return for approving the government's deal with the EU, or impose it in the event of 'no deal' to avoid the UK crashing out without a deal.
  • Some politicians have advocated a 'yes/no' referendum on the deal, but this would be unwise. The report also dismisses a two-stage poll, as some others have proposed, and concludes that a 'deal' vs. 'no deal' poll is unlikely.
  • Three question formats are more viable: 'deal' vs. 'remain', 'no deal' vs. 'remain' (if no deal is reached) or a three-option poll on 'deal' vs. 'no deal' vs. 'remain'.
  • The franchise for a referendum should be the same as in June 2016, to avoid the risk that a changed franchise alters the result.
  • Referendum regulation should be updated to account for online campaigning.
  • Five scenarios for a referendum are set out, with a first possible polling day in May 2019.

Proponents of a second referendum argue that, with parliament so divided on the UK's future, the public should be given the opportunity to decide whether or not to accept the deal the government has negotiated once the details are known. The Constitution Unit has no position on Brexit or on whether a further referendum should be held, but seeks to inform debate about the practicalities.

Co-author Dr Alan Renwick, Deputy Director of the Constitution Unit (UCL Political Science), said: "The principle of a further referendum on Brexit is likely to remain controversial, so it is of utmost importance that the process should command the maximum legitimacy. If the result is to be accepted by those on all sides, every effort should be made to ensure the referendum campaign is fair, the poll is properly conducted, the options put to the referendum are clear, and the question allows voters to express their preferences unambiguously."

Co-author Professor Meg Russell, Director of the Constitution Unit (UCL Political Science), said: "In the British system anything is possible given the political will. The current level of interest in a further referendum on Brexit makes it vital that serious consideration is given to all possible scenarios, including which would work best and which would be most problematic. As events remain unpredictable, and may unfold quickly, it is possible that politicians will need to take rapid decisions, and we hope that our report can guide sensible and responsible decision-making."

Commenting on the new UCL report Professor Anand Menon, Director of UK in a Changing Europe (the organisation with which the report is joint published), said: "As ever, the details matter. While it is of course completely legitimate to debate and indeed campaign for, a second referendum, it is important that we are aware of the practical legal and constitutional rules that would determine how this might come about. This report spells these rules out clearly and comprehensively."

The conclusions summarised:

How long would it take to hold a referendum?
In order for a referendum to be held in the UK various processes must be completed:

  • Legislation - Primary legislation is needed to provide the legal basis for a referendum and to specify details that are not in standing legislation, such as the referendum question, timing and rules of conduct.
  • Question testing - the Electoral Commission must carry out question testing, which usually takes 12 weeks, while the bill is still in parliament.
  • Preparing for the poll - the Electoral Commission and local officials would need to prepare for administering the poll and regulating campaigns.
  • Regulated referendum period - the UK's referendum legislation - the Political Parties, Elections and Referendum Act - specifies a minimum 10-week campaign period.

There are clear uncertainties in the timescales, many of which are greatly dependent on politics. If both the government and opposition were willing to throw their support behind calls for a referendum a swift legislative process is possible.

This process must, however, accommodate the Electoral Commission's testing. If that could be compressed into around eight weeks, the bill might be approved within 11 sitting weeks. Including the time to prepare for polling day and conduct the campaign, the total time to stage a vote might be 22 weeks.

However this doesn't account for any obstacles, such as disagreement in parliament over key issues such the referendum question, or difficulties of testing and preparing for an unfamiliar question format such as a multi-option referendum.
Is it feasible to extend Article 50?

All the indications are that the EU would be willing to agree an Article 50 extension to allow the UK to conduct a referendum before Brexit is concluded. The UK government would probably hold a parliamentary vote to authorise a request to extend Article 50.

Even if an extension was agreed, there are various obstacles including the European Parliament elections, which are scheduled to take place from 23-26 May 2019.

In the context of Brexit it has been assumed that the UK will not take part, but if Article 50 was extended the UK could be legally obliged to hold the elections. A short delay might be possible, but ideally time should be left for elections by the end of June in the event that the referendum resulted in a UK vote to remain in the EU.

How could a referendum be triggered?

In order for a referendum to be triggered there would need to be a majority in parliament in favour of holding such a poll. How likely this is to come about would depend on a number of factors - including the political circumstances, whether a deal is reached, the nature of that deal, and how public opinion develops regarding both a second referendum and the UK's relationship with the EU. There is a precedent for parliamentarians to impose a referendum as a condition for passing a government bill, in the 1979 devolution referendums.

There are five scenarios through which a referendum could be triggered either on the government's initiative or against its wishes. These are outlined below:

  • Negotiated deal - 'meaningful vote' motion conditional on referendum. If a deal is reached, this will be parliament's first opportunity to vote on it. The government needs the approval of the House of Commons in order to proceed. The Commons could make its approval of the deal conditional on a second referendum.
  • Negotiated deal - EU (Withdrawal Agreement) Bill conditional on referendum. If the House of Commons approves the exit deal in principle without a referendum condition, the Bill to implement it could potentially be used to require a referendum before the legislation comes into force. This is perhaps most likely if the government has bought off dissent on the motion and promised future action that it has not delivered.
  • Negotiated deal - 'meaningful vote' motion rejected. If the House of Commons rejects the motion on the deal this will create an impasse. The government might offer a referendum as a way out, or try to bypass parliament and seek the public's direct support for the deal.
  • No deal - If no withdrawal agreement is reached between the UK and the EU the EU (Withdrawal) Act 2018 requires the House of Commons to consider a motion in 'neutral terms'. This could lead to parliamentary pressure, or the government itself might choose to call a referendum as a means of preventing an unintentional 'no deal' scenario.
  • Negotiations continue - Although there is a strict timetable for resolving the Brexit negotiations, there is always a possibility that this is delayed due to failure to reach agreement. In this case, any of the above scenarios could ultimately ensue, but after significant delay.

What should the referendum question be?

Three main options could be considered for inclusion in any further referendum on Brexit: leave the EU on the government negotiated terms, leave the EU without a deal, or remain in the EU. Some may wish to include a fourth option: 'reopen negotiations', but a referendum of this kind would be ill-advised as it could not settle the issue of the UK's relationship with the EU.

There are various question formats that could be considered including: single yes/no question, single two-option question, multi-option referendum or two-stage referendum. Considering the options there are three viable approaches:

  • In the case that no deal is done: a straightforward choice between no deal and remain would be logical.
  • If a deal is reached: many referendum proponents may favour a deal vs remain vote; this could cause dissatisfaction among leave supporters, though that would depend on the nature of the deal.   
  • Another option, if a deal was reached, would be a three-option referendum between the 'deal', 'no deal' and 'remain'. In this case. 'First Past the Post' would be inadequate as a voting system; the Alternative Vote system (where voters number the options in order of preference) seems best.

Some options are ruled out:

  • A 'yes/no' vote on the deal: this would be unwise as a 'no' vote would have unclear implications, making it difficult both for voters and for parliament to interpret.
  • A 'no deal' versus 'deal' referendum: this would frustrate remain voters, and be very unlikely to win parliamentary support, including in the Lords.
  • A two-stage referendum: as the report demonstrates, this format could cause difficult tactical voting dilemmas and regulatory challenges.

Setting the rules for the referendum

Any referendum would need to be conducted within a framework of rules. The UK has some standing legislation set out in the Political Parties, Elections and Referendums Act, but this leaves out some key issues.

One is the franchise for a referendum. The 2016 EU referendum included all those eligible to vote in UK parliamentary elections, plus members of the House of Lords and Gibraltar residents eligible to vote in European Parliamentary elections. Some might argue that 16 and 17-year-olds and EU citizens should have the vote in a future referendum. But the 2016 EU referendum did not extend the right to vote to these groups. Doing so now might undermine the legitimacy of this vote. Hence the franchise for any further referendum should be the same as in 2016.

The recent Independent Commission on Referendums conducted a comprehensive review of UK referendum regulation and made various recommendations for improvement. Some of these should be applied, particularly in relation to the transparency of digital campaigning, and the quality of information available to voters.

Putting it all together

Returning to the five scenarios above, the report concludes the following regarding timetables and their implications:

  • Making the 'meaningful vote' approval conditional on a referendum would be the quickest route, allowing a referendum as early as May 2019 if using a two-option format, or June 2019 if based on three options. The European Parliament elections could then be held, if the result was 'remain'.
  • Making the withdrawal agreement bill conditional on a referendum would delay matters, particularly if change occurred only when the bill was in the Lords - which would create problems for the European Parliament elections.
  • Defeat on the 'meaningful vote' motion could in theory be followed by quick action, but in practice might descend into political wrangling.
  • If no deal is reached a referendum might still be possible by June 2019.
  • If negotiations continue beyond January 2019, Article 50 would need to be extended and the European Parliament elections held before the outcome was known.

The authors conclude that an Article 50 extension of 6-9 months is probably required to accommodate a referendum and its aftermath. To avoid major problems with the European Parliament elections MPs need to take responsibility for pressing the government on a referendum (not leave it to the Lords), and do so as early as possible in the process.


  • 'The Mechanics of a Referendum on Brexit', authored by Professor Meg Russell, Dr Alan Renwick and Jess Sargeant, UCL Constitution Unit, is available here.
  • Project page, including a blog series summarising the key findings.


  • Report cover

Media contact

Natasha Downes

Tel: +44 (0)20 3108 3844

Email: n.downes [at] ucl.ac.uk