Causes of the vote in favour of Brexit

'Leave' represented more popular positions

The 'Leave' campaign campaigned primarily on issues relating to sovereignty and migration, whereas the remain campaign focused on the economic impacts of leaving the EU. This choice of key positions is significant since Ipsos MORI survey data on which issues Britons felt to be 'important issues facing Britain today' shows that immediately prior to the vote, more people cited both the EU (32%) and migration (48%) as important issues than cited the economy (27%).

Sovereignty

On the day of the referendum Lord Ashcroft's polling team questioned 12,369 people who had completed voting. This poll produced data that showed that 'Nearly half (49%) of leave voters said the biggest single reason for wanting to leave the European Union was “the principle that decisions about the UK should be taken in the UK”.

Immediately prior to the vote, Ipsos MORI data showed that Europe was the third most highly ranked problem by Britons who were asked to name the most important issues facing the country, with 32% of respondents naming it as an issue.

Immigration

Lord Ashcroft's election day poll of 12,369 voters also discovered that 'One third (33%) [of leave voters] said the main reason was that leaving “offered the best chance for the UK to regain control over immigration and its own borders.”'

Immediately prior to the referendum data from Ipsos-Mori showed that immigration/migration was the most cited issue when Britons were asked 'What do you see as the most/other important issue facing Britain today?' with 48% of respondents mentioning it when surveyed.

In the decade before the Brexit referendum there was a significant increase in migration from EU countries, as outlined by the Migration Observatory:

'Inflows of EU nationals migrating to the UK stood at 268,000 in 2014, up from 201,000 in 2013. EU inflows were mainly flat for the 1991-2003 period, averaging close to 61,000 per year.'

According to The Economist, areas that saw increases of over 200% in foreign born population between 2001 and 2014 saw a majority of voters back leave in 94% of cases. The Economist concluded 'High numbers of migrants don’t bother Britons; high rates of change do.' Consistent with that notion, research suggests that areas that saw significant influx of migration from Eastern Europe following the accession of 12 mainly Eastern European countries to the European Union in 2004 saw significant growth in support for UKIP and more likely to vote to leave the European Union.

Age of voters

It has been argued that the result was caused by differential voting patterns amongst younger and older people. According to Opinium, 64% of eligible people aged 18–24 voted, whereas 90% of eligible individuals over 65 voted.

The 'order versus openness' divide

Academic Eric Kaufman notes the relatively strong correlation between a voter's support for the death penalty, and their choice to vote 'leave'. He says that this highlights a social division that he calls 'order versus openness'. He further argues that 'The order-openness divide is emerging as the key political cleavage, overshadowing the left-right economic dimension'.

Data from the British Election Study shows that support for the death penalty was a more reliable predictor of voting behaviour than any standard demographic measure of age, income or social class.

The 'left behind'

Matthew Goodwin and Rob Ford coined the term 'The Left Behind' to refer to 'older, white, socially conservative voters in more economically marginal neighbourhoods'. Analysing data the day after the Referendum, Ford concluded that 'Such voters had turned against a political class they saw as dominated by socially liberal university graduates with values fundamentally opposed to theirs, on identity, Europe – and particularly immigration.' This was described in as "if you've got money, you vote in... if you haven't got money, you vote out". The left-behind hypothesis is furthered using data on the EU referendum result across electoral wards level as well as across local authorities, suggesting that especially areas with high degrees of social deprivation and low educational attainment strongly voted in favor of leaving the EU.

Britons felt less integrated with the EU than other European citizens

Academics James Dennison and Noah Carl argue that 'the most important phenomenon to be explained vis-à-vis the referendum result in our view is that a sizable [sic] Eurosceptic faction has remained extant in Britain over the last four decades'. Using data from the Eurobarometer survey they showed that fewer Britons considered themselves European than any other EU nationality. Furthermore, they show that British trading patterns, capital flows and emigration patterns were the least Europeanised of any EU member state.

General identity issues

The World Economic Forum 2017 acknowledged in its Global Risks Report that "the Brexit and President-elect Trump victories featured (...) appeals to sovereignty rooted in national identity and pride" and that it would "be challenging to find political narratives and policies that can repair decades-long cultural fault-lines".

Lies and misleading information

Both sides in the referendum have been accused of using deliberate falsehoods during the campaign. Perhaps the most commonly criticised claim by the Leave campaign was that voting to leave the EU would allow for increased spending on the NHS of £350m a week.

Vote Leave claimed that the UK's contribution to the EU is £350 million per week. The Treasury's own statement of the UK's contribution to the EU is that the Net amount is £6.27 billion per annum. Divided by 52, this is approximately £120 million per week (NET amount). Sir John Major claimed that Vote Leave had deliberately misled voters by using the Gross contribution to the EU, £360 million. The Gross contribution is the total contribution paid, not including any discounts and rebates. The UK currently gets a 40% discount from the Gross contribution which was negotiated by Margaret Thatcher in the 1980s (worth about £144 million) plus various agricultural, economic development and scientific research 'rebates' (worth approximately a further £96 million).

The Leave side allege exaggeration and falsehood in the Remain campaign's predictions of economic disaster arising from leaving the EU, which was termed 'Project Fear', culminating in the threat by George Osborne (then Chancellor of the Exchequer) to impose emergency tax increases in a 'punishment budget' after a 'Leave' vote. After the vote, no such budget was brought forward.

Elements of the campaigns have been identified as exemplifying "post-truth politics", in which debate is framed largely by appeals to emotion rather than the details of policy or objective factual analysis.

Branding and wording choices

It has been argued that the 'Leave' brand was stronger and more effective than the 'Remain' brand. According to Mike Hind, a marketing professional, 'The Britain Stronger In Europe brand was stillborn. On the basis of preparation, presentation and messaging, it deserved the kicking it got.' Additionally behavioural practioner Warren Hatter argues that 'Leave' as a word places a lower cognitive load on observers than 'Remain a member of'.

Prospect theory

Economics writer Chris Dillow has argued that, amongst other factors, Prospect Theory may explain in the surprising willingness of many voters to take a path widely viewed as the more risky of two (change vs status quo). In his words Prospect Theory 'Tells us that people who feel they’ve lost want to gamble to break even. This is why they back longshots on the last race of the day or why they hold onto badly performing stocks. The thing motivated many Leavers. People who had lost out from globalization, or felt discomfited by immigration, voted Leave because they felt they had little to lose from doing so.'

Decision not to impose tougher migration restrictions

It has been claimed that the role of migration as a key factor in driving voting behaviour at the referendum originates from the relatively high levels of net migration into the UK in the last decade. In particular it is claimed that the decision not to impose restrictions on EU migrants after the addition of the 'A8' (Eastern European) countries to the EU in 2004 (at a time when other European countries did impose such restrictions) contributed to a spike in migration levels that underpins contemporary voter attitudes.

European Migrant Crisis

President of the United States Donald Trump stated that German Chancellor Angela Merkel's decision to open her country's borders for more than a million refugees and illegal immigrants was a "catastrophic mistake" and "the final straw that broke the camel's back", allowing the Leave campaign to win. As a candidate for the office, Trump already made similar statements prior to the referendum and after it, for example at a rally in Ashburn, Virginia, where he also suggested that more countries would leave the EU because of Merkel's decision.

Pro-Brexit party UKIP used images from the migrant crisis during their campaign, a decision that prompted criticism from Leave and Remain supporters.

The media

The Guardian journalist Jane Martinson noted that many of the UK's biggest selling newspapers, The Sun and the Daily Mail in particular, but also including The Daily Telegraph and Daily Express, have been arguing for Britain to leave the EU for many years. Documentary film "Brexit: The Movie" by Martin Durkin also presented the case in favour of Brexit.

The BBC was also criticised by many remain-supporting pundits for false balance which helped give the leave campaign credibility. It gave equal platforms to experts advocating both sides of the debate, even though experts in nearly every area overwhelmingly supported continued EU membership. It was also accused of taking its agenda from the newspaper industry - since the highest-selling papers were pro-Brexit, this further warped its neutrality.