How could a second Brexit referendum be triggered?

jess_sargent.000alan_renwick.000download.001With ‘exit day’ less than six months away, public debate about a second Brexit vote continues. In the third of a series of posts on this topic, Jess Sargeant, Alan Renwick and Meg Russell outline the key decision points and processes by which MPs or the government might choose to trigger a second referendum.

In our previous blogpost we considered how long it would take to hold a second referendum on Brexit, concluding that an extension to Article 50 would almost certainly be required. The length of the necessary extension would depend on when the referendum was triggered. Calling a referendum requires a majority in parliament, and whether such a majority exists will depend on political and circumstantial factors. But by examining the process of Brexit we can identify a number of key junctures at which a decision to hold a referendum could be made.

What steps must take place before the UK leaves the EU?

According to Article 50, an agreement setting out the arrangements for withdrawal, taking account of the UK’s future relationship with the EU, should be concluded within two years. If no such agreement is ratified before 29 March 2019, the UK will leave with no deal, unless the Article 50 period is extended. For the UK to ratify the deal, three parliamentary steps must first be completed:

  1. Parliament must approve the deal. The EU (Withdrawal) Act 2018 requires the House of Commons to pass a motion, often referred to as the ‘meaningful vote’, approving the withdrawal agreement and the framework for the future relationship. This motion is expected to be amendable.

    • If the motion is passed, the government can proceed to the next step.

    • If the motion is not passed, the government must then set out how it intends to proceed. The Commons is then due to consider the plan through a motion in ‘neutral terms’, which may well not be amendable.

  2. The European Union (Withdrawal Agreement) Bill must be passed. The government will need to pass primary legislation to give the withdrawal agreement domestic effect. The government cannot ratify the deal until this is done.

  3. The Constitutional Reform and Governance Act 2010 (CraG) procedure. The withdrawal agreement will also be subject to the usual procedure applied to treaties, which can happen concurrently with the steps above. The government must lay the treaty before parliament, which then has 21 days to object to ratification. If the Commons objects it can delay ratification indefinitely.

All of this supposes that a deal is reached. If no withdrawal agreement is reached by 21 January 2019 the government must lay a statement before parliament outlining how it intends to proceed. Then a motion must be considered, again due to be in ‘in neutral terms’ and so probably unamendable.

What are the possible routes to a second referendum?

As discussed in a previous blogpost, primary legislation is required to provide the legal basis for a referendum. One possibility is clearly that the government could change its mind, perhaps as a result of a large shift in public opinion, and introduce a referendum bill. At present, this looks unlikely: Theresa May has firmly ruled out a second referendum. Theoretically, it would also be possible for a referendum to be mandated by a Private Member’s Bill, but this even less likely given the timescale and that few such bills ever succeed.

Most likely, if a majority in parliament favoured a second referendum, would be for parliament to force the government’s hand. There is a precedent for parliamentarians to impose a referendum as a condition for passing a government bill: the 1979 devolution referendums came about in this way. As outlined above, parliament will have multiple opportunities to vote on the withdrawal agreement. These could be used to require a referendum, either by defeating the government directly, or by extracting concessions. The potential flashpoints where a referendum might be called are outlined in the diagram below.

Parliament process w referendum flow diagram

‘Meaningful vote’ motion

If a deal is reached, the ‘meaningful vote’ motion will be parliament’s first opportunity to vote on it. The government needs the Commons to approve the deal in order to progress onto the next step – which clearly gives MPs important leverage. If a second referendum has enough support, the Commons could make its approval of the deal conditional on a referendum. Either the motion could be amended, or dissenters could agree to support the deal in exchange for a government commitment to call a referendum. The Lords will debate the agreement too, but only on a ‘take note’ motion that will not permit amendments.

If the Commons refused to approve the deal, procedural considerations could provide an incentive for ministers to propose a referendum. Parliamentary procedure prevents a motion on a question that has already been decided from being brought forward in the same parliamentary session. Hence if the government fails to get support for the ‘meaningful vote’ motion in the first instance, and wants to make a second attempt in order to proceed with the deal, a subsequent motion would need to be substantively different. Making the deal subject to approval in a referendum could be one way of fulfilling this requirement, as well as of buying off dissenters.

EU (Withdrawal Agreement) Bill

Even if the House of Commons approves the exit deal in principle without a referendum condition, the subsequent EU (Withdrawal Agreement) Bill 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, or if there is a significant delay between the motion and the introduction of the bill, during which public and parliamentary opinion changes.

The bill’s Commons second reading will provide MPs with a second opportunity to ‘veto’ the deal should they wish. At this point a ‘reasoned amendment’ could make the continued survival of the bill dependent on a referendum requirement, or (as with the motion, discussed above) the threat of a second reading defeat could be used to force the government to volunteer such a commitment. If the bill survives, amendments requiring a referendum could also be added at committee stage. Amendments could also be added in the Lords, whose first opportunity this would be to place conditions on supporting the deal. Any such amendments would need subsequent Commons approval.

Failure to agree a deal

If no withdrawal agreement is reached between the UK and the EU, or if parliament refuses to approve the deal, the EU (Withdrawal) Act 2018 requires the House of Commons to consider a motion in ‘neutral terms’. This wording was an attempt by the government to ensure that these motions were unamendable, but it eventually accepted that, as a matter of parliamentary procedure, the status of such motions would be a decision for the Speaker. Either way, there is no legal requirement for such a motion to be passed before Brexit, so it could be a poor vehicle for extracting concessions via amendment. Nonetheless, in this difficult political scenario, MPs could find other ways of forcing a vote on a referendum if necessary (e.g. through an opposition motion) and while not legally binding, this would be very difficult for the government to ignore.

Indeed, in this kind of political environment, the government itself might choose to call a referendum as a means of preventing an unintentional ‘no deal’ scenario – particularly if there were clear signs of change in the parliamentary or public mood.

If the government does not come to a decision to hold a referendum on its own, parliament could use other parliamentary mechanisms such as opposition day and backbench dates to force a vote on the issue, and put further pressure on the government.


We have identified a number of scenarios in which a referendum could be triggered, either on the government’s initiative, or against its wishes. However, all ultimately depend on there being a parliamentary majority in favour of such a vote. How likely all this becomes will depend on a number of factors – including 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. At this point in time, campaigners for a ‘people’s vote’ may not have sufficient Commons support to force such a change, but there is much that remains unknown. Notwithstanding Theresa May’s current firm stance against a further referendum, the path to Brexit is highly unpredictable, and another public vote remains possible.  

This is the third in a series of posts on ‘The Mechanics of a Further Referendum on Brexit’. Further blogs on this topic will be added in the coming weeks: to see all posts in the series, visit our project page

About the authors

Jess Sargeant is a Research Assistant at the Constitution Unit. 

Alan Renwick is Deputy Director of the Constitution Unit.

Meg Russell is Director of the Constitution Unit.

6 thoughts on “How could a second Brexit referendum be triggered?

  1. Pingback: Could Article 50 be extended to allow for a second Brexit referendum? | The Constitution Unit Blog

  2. Pingback: If there’s a second referendum on Brexit, what question should be put to voters? | The Constitution Unit Blog

  3. Pingback: Brexit Highlights 3 – 9 September 2018 | Middle Temple Library Blog

  4. Pingback: How could a second Brexit referendum be triggered? – The Constitution Unit Blog – Cllr Craig Hannaway

  5. Please discuss the far simpler alternative – see Lord John Kerr’s 10 November 2017 lecture.

    [Full text and French and German Translations in my book ‘The Four Brexiteers and the Fracturing of the West’ p197 – 220]

    I follow your discussions with much interest – thanks, John Pedler


  6. Pingback: How long would it take to hold a 2nd EU referendum? - Sceptical Scot

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