For votes which can have extremely long-term consequences, (like changing the constitution) a simple majority vote is usually not enough. Such voting and referendums are not about electing a temporary leadership which can be easily changed in 4 years or even sooner. Therefore, it's common practice to require supermajority, for example:

  • over 50% of all people with a right to vote

  • over 2/3 of those who voted, with possible further constraints like a turnout of over 50%

Why wasn't supermajority required for the Brexit referendum? A vote which is close to 50% - 50%, (and it was foreseeable to be close to 50% - 50%) is highly depending on random chance: mood, weather, recent events which stir up emotions but are insignificant long-term, and other temporary factors which might change the result a percent or two in a very short time period. So one could argue that Britain let random chance and temporary mood to decide its long term values and strategies.

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    Don't know about "usually" in a global sense, but here in Switzerland constitution is changed regularly by small margins in popular votes. For example in February by 50k votes (of more than 3 million).
    – Nobody
    Commented Jun 24, 2016 at 14:03
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    @Nobody : If changing the constitution is such a frequent event in Switzerland, then it makes sense for a simple majority to be enough. However, when the consequences are long term and impossible or very hard to change, it might be a completely different situation. I'll have to study the Swiss constitution and compare it to other countries, but it might be that the Swiss constitution contains much more concrete things, things which other countries don't put into their constitutions but into laws, preserving a small and generalist constitution with a much smaller need to change it often.
    – vsz
    Commented Jun 24, 2016 at 14:15
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    I just took a look at the German Grundgesetz and it seems to be longer than the Swiss one, but they still change it less often. And it's not really fast to revert a change in Switzerland. Don't think that was done recently. It takes several years and lots of effort before a vote on a topic can be enforced by the people, and the same again to reverse it.
    – Nobody
    Commented Jun 24, 2016 at 14:34
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    Related to this, there's a petition that's quickly gained nearly two million signatures at the time of writing, which demands the UK "implement[s] a rule that if the remain or leave vote is less than 60% based a turnout less than 75% there should be another referendum."
    – KenD
    Commented Jun 25, 2016 at 16:54
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    Was that higher standard required when Great Britain joined the EU?
    – lazarusL
    Commented Jun 29, 2016 at 13:41

10 Answers 10


The voting threshold necessary to prompt the exit process was never actually decided at all as such prior to the referendum, but assumptions were made by politicians and journalists about what would be politically acceptable to an emergent notion of popular sovereignty. The law establishing the referendum did not specify any resulting action or level of vote necessary for action, and nor did any secondary regulations, nor the legislation for referendums in general.

The nearest Parliament seems to have got to thinking about the matter was in rejecting the SNP's amendment that would require a supermajority or 'quad lock', whereby a Scottish vote to leave (which in the event did not happen) was needed for action by the UK. The debate as a whole seems to indicate that little thought was given to the basis for a referendum within an unwritten constitution. This lack of clarity contributed after the event to more than four million people signing a petition for a second referendum requiring a clearer majority, and alternative suggestions by Geoffrey Robertson QC that MPs should overturn the perceived result: "Democracy has never meant the tyranny of the simple majority".

(However, there has also been some dispute about whether MPs technically even need to vote on exit - possibly against their own opinion - before the executive triggers the irreversible Article 50, which itself refers to the UK's 'own constitutional requirements', unclear as they are. It has been suggested that there are moral reasons for MPs to reflect the simple majority outcome, but Dr Yossi Nehushtan says it is "morally-politically inconceivable to treat a 52% majority decision in a referendum as authoritative with relation to constitutional principles".)

So where does the legitimacy of a 50% threshold come from? The Conservative manifesto 2015 says

We will negotiate new rules with the EU [specifically about benefit entitlement]... We will then put these changes to the British people in a straight in-out referendum on our membership of the European Union by the end of 2017.

'Straight in-out referendum' implies a referendum with two choices; this was designed to appeal to voters who liked the sound of 'in' as well as 'out'. It doesn't say anything about threshold, but it could be argued that it gives equivalence to each outcome, rather than recognising one of them as a more significant constitutional change. (Only Conservative MPs could be held to the wording in their manifesto.) A month before the referendum, Prime Minister David Cameron said "Obviously a referendum is based on a simple majority", but as the existence of the question implies this is far from obvious. It does seem that most MPs had made the same assumption by this point, and the question is why. Previous referendums, such as the Scotland devolution referendum 1979 had a threshold of 40% of eligible voters, which it failed to meet despite meeting a simple majority.

One likely influence was the most recent UK-wide referendum, on Alternative Vote. Although clearly a fundamental constitutional change, the Liberal Democrat party negotiators wanted a definite prospect of electoral reform and to be seen as equal partners in it. The coalition agreement therefore stated:

Both parties will whip their Parliamentary Parties in both Houses to support a simple majority referendum on the Alternative Vote (emphasis added)

This subsequently entered law as s8 of the ensuing Act which unlike the EU referendum did clearly specify how the counted votes were to be interpreted, and may have set a precedent in many MPs' minds. Also note that the Conservative party tends to oppose any constitutional change, and have a fixed idea of decision-making procedure and little time to spend on STV or modern electoral systems. Therefore when the Prime Minister of the time said 'obviously' it was not merely rhetoric, but reveals a mindset formed in an environment not familiar or patient with constitutional reasoning and most concerned with precedents within his terms of office.

There is also the question of whether leaving the EU is a constitutional matter (where a civil society organisation would typically require a two-third majority). I've heard it claimed (by a Leave supporter) that Remain supporters deny that the EU membership affects national sovereignty and therefore it is not a constitutional matter. On the face of it, the way EU Regulations enter force (as part of an evolving trade treaty) without the intervention of the UK parliament, obtaining some legitimacy from election of MEPs, is a part of the current constitution. A professor of law at QMUL has no doubt the decision to leave is a constitutional issue, and mentions the possibility of a second referendum on the terms of an exit, although it's not clear what would happen if the terms are rejected and Article 50 has been triggered.

So we're left with a potential conflict between Parliamentary sovereignty on the one hand and on the other a 51.9% majority of voters on a higher turnout than the last general election. To some minds, avoiding that conflict to maintain the legitimacy of the political system is a more important moral imperative than anything else, which would have been a good argument for a sufficient threshold to ensure Parliament was aligned with the 'result'. Nat le Roux has written one of the best summaries of the ramifications of 'paradoxes of legitimacy' caused by advisory referendums. The AV referendum was binding, not advisory, but had a 50% threshold. The EU referendum was advisory, not binding with an undefined threshold, assumed to be 50%, which is 'potentially destabilising'. The idea of the 'will of the people' is used by Conservative Leave MPs to strengthen their position: they may believe Leave stabilises the Conservative party itself, which after all was one purpose of the referendum.

tl;dr: cock-up.


The UK has a political history and tradition which has enshrined the concept of parliamentary sovereignty to almost religious levels. Among other concepts this enshrines the view that there is no binding method for one sitting Parliament to bind a future Parliament irrevocably to a decision, and these decisions are made by simple majority of those MPs present in the house.

Meanwhile the UK has very little tradition of national referendums (the recent EU referendum was the third) and only one of these (the 2010 referendum on the Alternative Vote) was written in such a way that its result was legally binding. As such, the votes have always been simple majority on a binary question, following the approach of Parliament.

An argument given for this approach is that when constitutional mistakes happen and are generally seen to have happened, it is unnecessary to obtain a supermajority to apply a fix. Fundamentally you can think of this as one extreme in a spectrum of constitutional approaches ranging from "easy to change and fast to react" to "hard to change, but slow to react.

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    If the need for change is "generally seen," it should be easy to get a supermajority. When a major change with long-lasting effects is highly contentious, supermajority requirements help ensure that such steps are only taken when it's clear that most people really want to take the step. The argument that major changes are always "generally seen" to be mistakes so that "it is unnecessary to [require] a supermajority to apply a fix" doesn't make sense in an application where changes can be so major and long-lasting.
    – WBT
    Commented Jun 24, 2016 at 17:30
  • 1
    True. Equally the absence of the application change can have major and long-lasting effects. But the choices in the UK system have to be seen in the light of the doctrine of parliamentary sovereignty, just as, for example, decisions in the US have to be seen in the light of checks and balances.
    – origimbo
    Commented Jun 24, 2016 at 18:25
  • @origimbo And in a very real sense the 2010 referendum could easily have become non-binding; all it would've required is Parliament amending the referendum act to remove the obligation to enact it before that happened, or simply waiting till it is enacted then immediately repealing the enactment.
    – gsnedders
    Commented Nov 11, 2016 at 15:04

I suppose the answer to the question is that David Cameron, the PM who campaigned on a manifesto calling for an EU referendum by 2017, was confident enough that remain would win. As such, he went for the referendum without bothering with a supermajority. A mistake: a close result on a critical issue on a simple majority was always going to be divisive.

  • 1
    Also I suspect this will be deleted for being too speculative, I am inclined to agree.
    – bon
    Commented Jun 27, 2016 at 17:30
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    Also a "undecided vote" would have left the Conservative party will all of the interval problems. Commented Jun 28, 2016 at 14:45

Hubris. Cameron needed the referendum as bartering material for pulling other EU members over the table regarding UK-only conditions, exceptions, and negotiations. For that to work, there needed to be a significant apparent danger of the referendum to succeed.

He overbid his hand.

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    This says that it was chosen precisely because it could have gone Leave. It's not cited and may not be true, but it is certainly responsive to the question.
    – Brythan
    Commented Jun 28, 2016 at 20:56

(I am from The Netherlands, but I feel I have enough interest in this matter to say something on this subject. Excuse my English, which is not perfect at all). Even if Cameron was confident, Cameron took a huge risk. Indeed, in many countries (and I think also in the UK) a qualified majority such as a 2/3 or 3/5 majority is required for certain important decisions. And that is for a good reason, as some decisions should not easily or lightly be taken. Influences that do not really reflect the will of the people (such as the weather or someones mood or the issues of the day) should be ruled out as much as possible when it concerns these decisions. I still have not found an answer as to why Cameron emphasized that a simple majority outcome of the referendum is decisive for the UK parliament to decide to leave the EU and frankly, I do not understand it. Also, I would not understand it if the outcome of this referendum would be considered a clear will of the UK people. A 51.9 majority just does not reflect such clear will. It reflects uncertainty and division. The outcome may have been different a day before or a day after. This is not a basis for important and far-reaching decisions like leaving the EU, especially as not only UK citizens will feel the consequences, but also the rest of the EU and even the world. Anyhow, I hope that EU and UK will keep on cooperating in many ways and wish you all the best (I love both EU and UK). May v M.

  • 3
    Although I agree with your points, this is not an answer to the question. You describe what it is also described in the question: why in similar situations, usually a system other than a simple majority is applied. But the question was that despite these issues, why did they decide on a simple majority.
    – vsz
    Commented Jun 28, 2016 at 13:35
  • You're right vsz. I should have posted it as a supportive comment to the question instead as an answer (Im new on this platform). I have no answer and I wonder if there is one (in other words, I wonder if the idea of a qualified majority was given a thought by the initiators of the referendum at all...)
    – May van M.
    Commented Jun 28, 2016 at 14:21
  • To clarify a bit more: This specific referendum is legally not binding, but is consultative. Therefore, it is not useful to attach more conditions to the votes of the referendum itself, than a single majority vote.The decision to invoke art. 50 of the Lisboa treaty in view of the ref is up to the government - not to the referendum. This decision is now a matter of politics - not of law or written conditions. Point is, that Cameron made a firm promise to invoke art. 50 by saying the ref is decisive without further conditions. I have no answer as to why he did that.
    – May van M.
    Commented Jun 28, 2016 at 16:15
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    He did it in a desparate and incredibly irresponsible bid to save his political career? Though right now we just don't know if this is the best thing that could have happened, and leads forward to a better built future rather than descending Europe into poverty and chaos.
    – Arwin
    Commented Sep 16, 2016 at 10:08

This question was actually asked in Parliament at the time: Should the result be required to be a supermajority?

The answer given was: No, because it will only be an "advisory" referendum, not a "binding" one.

Despite that, a pamphlet issued by the Government stated, in effect, that the referendum result would be considered binding, and subsequent policy has reflected that, with a very rapid triggering of Article 50.

I think it could be argued that Parliament was misled on that very important question, just as the public was seriously misled on the likely consequences.


The short answer is one of the following:

  • Either that they are mistaken, and simply don't know of the shortcomings of a simple majority vote.
  • Or that they want to deliberately take advantage of the fact that votes fluctuation exists. This gives manipulators of votes (e.g. government and special interests) the ability to use the media to engineer momentary public opinion fluctuations right around time the votes are cast with the objectives of walking the public towards the outcome that the manipulators want.

    • This is very similar to the following case of measuring average population height: imagine if every person jumps right around the time we measure his height. This way, during the measurement, people appear much taller. Think of the opposite (people sit down right around measuring their height). Of course, the actual impact is only momentary, but the measurement is permanent. Manipulators use this problem in voting systems to somehow cheat around by taking advantage of momentary vote bursts.

Check my post here. Basically, if we wish better voting methods, we need to ensure that we remove the momentarily fluctuations out of the system so that we give the manipulators less options to unethically twist voting outcomes.


A referendum is the most democratic tool there is. It lies within the responsibility of those who vote to know what they vote about and what consequences there could be. I personally envy states as Switzerland (or the UK in that matter) where important matters can be decided by the people of the country and not exclusively by politicians who are so much influenced by mighty interest groups.

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    The democracy in the tool relies on those voting to understand the issue at hand, the likely effects, and what the outcome would be as you state. The evidence is that the majority of those who took part in the vote (irrespective of which side they took) did not fully appreciate the role membership of the EU in British life nor are they free of influence from pressure groups (like most british newspapers for example.) Commented Aug 30, 2017 at 23:10

Ok - so why was the vote and consequential action undertaken on a simple majority. It can only be for 2 reasons - Ineptitude on the part of our leader and a failure of our parliament process at the time. What this simple explanation does not address is how the rigour and transparency of our parliamentary process allowed the devastatingly flawed act of judgement by David Cameron to be given the credence and political traction to allow such an abrogation of public duty to be entrusted to the public without deployment of a properly considered and weighted supermajority. With Vote Leave activists now being found to have breached funding rules and receiving fines for serious funding irregularities, shouldn't the integrity of the simple majority result now be cast in sufficient doubt as to legally justify the striking out of the result of the referendum and being the legal justification of a new referendum - with a supermajority properly considered and included. If the funding rules were breached and an unfair advantage gained by the leave argument, how can we be sure that even the simple majority reflected the wishes of the people? This is too important to ignore.


Referendums are not a frequent or well-specified part of the UK's uncodified constitution. Each referendum is conducted on the basis of a separate act of Parliament. Furthermore, they are not binding; it's possible to construct a "self-executing" one, a body of law that will only be enacted if a particular referendum result is achieved, but any referendum can be overridden by act of Parliament.

Furthermore, the UK doesn't have a tradition of supermajority being required for any law - all law is by simple majority. Parliament can enact whatever it wants. Prior to R V Factortame, any act of Parliament over-rides any other.

There is no standard, prescribed electorate for referendums in the UK, let alone what approval rules are required. The 1979 Scottish Devolution referendum had a turnout requirement, which prevented it taking effect on a 52% victory. None of the subsequent ones did. Why? Well, one possible argument is that it didn't "settle the issue" and instead created a "stolen" narrative that persisted.

The 2014 Scottish independence referendum allowed EU nationals resident in Scotland to vote, as well as 16-year-olds. The subsequent Brexit referendum did not. Why? That's simply where the politics ended up.

A meta-problem is that the UK is extremely bad at handling "constitutional" issues. Joining the EU has forced some of these to be developed, simply because all other EU countries have constitutions. There have been a number of cases in Germany where its courts have ruled that the local constitution has precedence. (See section 3 of https://www.brugesgroup.com/images/papers/eulawsupremeovernationallaw.pdf - this is a very pro-Brexit source but also well-footnoted, and good descriptions of the system that aren't in German seem to be hard to find.)

There is also a strong belief that a close referendum result should "settle" an issue, allowing the narrowly overruled minority to be completely ignored for years after.

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