A referendum is not like an election. While the two sides of the campaign produced lots of literature supporting their view, there wasn’t anything like a manifesto as such. How could there be, given those leading the campaigns were not those who would end up actually implementing the decision? As far as the referendum was concerned, Brexit did indeed just mean Brexit – no more and no less. Nothing on the ballot paper said it was specifically this sort of Brexit or that sort of Brexit.

This has left a certain void, and one that politicians and others have sought to fill. Naturally, they have largely attempted to do so with their pre-existing prejudices rather than evidence. To listen to some it would appear that Brexit was driven by people who wanted {insert policy idea that I wanted to begin with}. A lot of this has been around how important an issue immigration was to Leave voters, and too what extent this was an anti-immigration vote. The alternative argument is often that the vote was mostly driven by concerns about sovereignty and freedom.

At the simplest level, if you want to know why people voted for something… ask them.

In YouGov’s final poll they asked people to pick which one factor was most important to people in deciding how to vote. Among Leave voters the most popular answer was allowing Britain to act independently (45%), followed by immigration (35%) and the economy (8%). Full tabs are here.

Lord Ashcroft’s poll after the referendum asked leave voters to rank four possible reasons for the vote – sovereignty, immigration, the economy or the risk of future EU integration. 49% of Leave voters picked sovereignty as their first reason (78% as either their first or second answer), 33% of Leave voters picked immigration as their first reason (64% as either their first or second reason). These two issues dominate, but the structure of the question suggests that people couldn’t say “I didn’t care about this issue at all”, so its somewhat limited (tabs are here, the relevant questions are on page 256!)

In both of these examples sovereignty came top, followed by immigration. However, it’s possible that this was down to the particular options the pollster offered or the particular wording used in the question. One way of getting round this issue is to ask it as an open-ended question and allow people to say in their own words why they voted as they did – two other polls did this.

In Ipsos-MORI’s final poll they asked what issues would be important to people in deciding how to vote in the referendum, letting people pick more than one option. The interviewer then picked which category or categories matched their answer most closely. In this case immigration came top among Leave voters, picked by 54% (18% also said the cost of immigration on welfare and 12% said the number of refugees coming to Britain – though given people could choose more than one option these cannot be added together). The next highest option among Leave voters was 32% who said the ability of Britain to pass our own laws, followed by 19% who said the economy and 9% who said jobs.

The pre-election wave of the British Election Study did a similar thing, asking respondents to type in what the most important factor driving their vote was and coding it up later. Taking a word cloud of the responses gives one extremely prominent answer…

…but this is actually a little misleading. Once the answers are coded up individually sovereignty comes very narrowly ahead of immigration. Just over 30% of verbatim responses from Leave voters mentioned sovereignty or control in some way, just under 30% mentioned immigration in some way (the word cloud appears as it does because most people who mentioned immigration used the specific word immigration, but people who mentioned sovereignty used a variety of different terms like sovereignty, control, making laws and so on). Suffice to say, immigration and sovereignty were, between them, the main two issues driving the Leave vote.

Referendums and elections are complicated things, and the human beings who vote in them are even more so. Anyone who tries to boil down the referendum to one factor and say “this explains it all” will almost always be wrong. While the order of the two issues differs between polls, all the polling evidence is clear that Leave voters were most concerned about the issues of sovereignty and immigration, and anyone claiming they were motivated by one but not the other is very likely projecting their own views onto the voters.

While they were clearly the dominant issues, there are undoubtedly others too – for example, as John Curtice explores here, there’s a very strong correlation with views on the impact of Brexit on the economy too, so while immigration and sovereignty were strong factors in favour of Leaving, another important factor seems to be that most leave voters did NOT think that Brexit would bring economic damage. I should also give my usual reminder that people are not necessarily very good judges of what makes them vote. We are not particularly rational creatures and the way people vote at referendums and elections is not a dry comparison of policy offers or facts, but often a mixture of vague feelings, bias and heuristics – so things like a lack of trust in the traditional media and “experts” and a perception that the remain campaign were speaking for an out-of-touch establishment rather than ordinary people were probably also factors in driving the Leave vote.

In short – the factors motivating Leave voters are many and varied and 52% of the voters will, by definition, contain people with many, many different views and priorities. However, every effort to ask Leave voters why they voted to leave found sovereignty AND immigration as the clear big issues.