On the morning of 23 June 2016, Rosamund Shaw still wasn’t sure if she wanted Britain to leave the European Union. During the preceding weeks, she had been in turmoil. She absorbed a stream of negative stories about the EU in the Daily Mail, but wasn’t sure they were reliable. She trusted Boris Johnson, but loathed Michael Gove. Her family was divided. One daughter, who worked abroad, was a staunch remainer; the other an adamant leaver. Upending the usual age dynamic, her younger relatives complained of eastern European migrants costing them work, while her mother, who had lived through the second world war, felt that the EU had guaranteed peace in Europe. In the voting booth, Shaw finally made her choice: she voted leave. “To be quite frank, I did not believe it would happen,” she says. “I thought I’d put in a protest vote. The impact of my stupidity!”

As soon as Shaw saw the result the following morning, her heart sank. “I was in shock,” she remembers. “Even though I voted leave, I thought, ‘Oh no! This is terrible!’ Then all hell broke loose. The texts started flying. There was a massive fight on Facebook.”

Rosamund Shaw is a pseudonym. If she was identified, she says, it might inflame the bitter family row that has been raging since last June, and she still hasn’t told her remainer daughter the truth about how she voted. In the weeks after the referendum, she found herself feeling apologetic around EU migrants. “I feel I need to smile and talk to people who are waiting on me in pubs and cafes and say, ‘I’m really glad you’re here. I don’t want you to go.’”

A few months ago, Shaw was hospitalised after an accident. “That was the catalyst that brought me over strongly to remain,” she says. “Ninety per cent of the people who dealt with me were immigrants. I thought, what the hell are we doing? This is wrong on so many levels. We’ve opened Pandora’s box and that distresses me beyond measure.”

How does she feel now about her decision on 23 June?

“I feel horrified with myself that I was so gullible,” she says heavily. “I feel ashamed.”

***

Seventeen months after the referendum, the regretful leave voter is the dog that hasn’t barked. Since the result came through, remainers have anticipated a significant U-turn for many reasons: the protest voters who didn’t expect leave actually to win; the ones who felt misled by the promise of £350m a week for the NHS; the ones spooked by the plunging pound and, more recently, the faltering negotiations. Surely, they felt, enough voters would see the error of their ways to weaken the mandate for hard Brexit at the very least.

Humans do not instinctively enjoy changing their minds. Admitting that you were wrong is a destabilising experience

In fact, the figures have remained stubbornly static. In April, the British Election Study surveyed almost 28,000 voters and found that 11% of leave voters expressed regret – but so did 7% of remain voters. While opposition to Brexit is hardening among remainers – according to YouGov, the number who believed the referendum result should be honoured plummeted from 51% to 28% between June and October – movement from leave to remain is slow. In October, the proportion of voters who felt that Britain had made the wrong choice reached a new high of 47% versus 42% (the rest weren’t sure). But that’s not yet enough to change the political calculus. However the question is phrased, the level of regret remains consistent with that following the 2015 election. The people featured in this article are a minority.

“It’s not that nobody is changing their minds,” explains Joe Twyman, co-founder of YouGov. “Very few are, and when they are, they’re cancelling each other out, so the aggregate level change is very small.”

For experts in voter behaviour or cognitive science, however, this is unsurprising. Humans do not instinctively enjoy changing their minds. Admitting that you were wrong, especially when the original decision has huge ramifications, is a painful and destabilising experience that the brain tends to resist. Research into this kind of denial has given us concepts such as cognitive dissonance and confirmation bias.

“When you have a strong view about something, you’re likely to reject information that’s contrary to your view, reject the source of the information and rationalise the information,” says Jane Green, professor of political science at the University of Manchester and co-director of the British Election Study. “We select information that’s consistent with our views, because it’s more comfortable and reaffirming.” In fact, it’s physically pleasurable. Some recent studies of confirmation bias indicate that consuming information that supports our beliefs actually produces a dopamine rush.

In the case of the referendum, there are additional factors that make it even harder for people to change their minds. For one thing, the decision in the voting booth feels irrevocable. Someone who regretted, say, voting for the Liberal Democrats in 2010 could choose another party in 2015, but someone who feels bad about voting leave doesn’t (yet) have a second chance. This makes life difficult for pollsters. While they can ask voters how they would vote if there were a general election tomorrow, a question about a hypothetical second referendum is controversial. Brexit opponents, including Nick Clegg and Alastair Campbell, have argued that another referendum on the terms of the deal would be legitimate, but many voters see this as a devious attempt at a do-over.

When I went to the cafe, I felt very bad. There are Europeans working there and I hadn’t even thought about them

Then there is the tribalism, which is intense. The referendum formalised a deep cultural divide. “We know that party identification is in decline,” Green says. “It could be the case that leave or remain is a more important identity.” In many cases, the vote manifested beliefs that had been entrenched for decades. “The campaign mattered, but it revealed divisions with deep roots,” she adds. “When people have held a view for a long time, that’s harder to change in the short run.”

To admit that you now believe you were wrong requires unusual honesty and courage; publicly to admit it takes even more. I contacted dozens of leave voters who had expressed regret on public forums. Many didn’t reply. Some agreed to talk, and then got cold feet at the last moment. A few, fearful of stoking tensions with relatives and colleagues, or of attracting abuse from Brexiteers, would only be interviewed anonymously. Others wouldn’t risk even that. “I have too many related family and business issues to deal with around this subject,” one told me. “Any hint would damage me even more.”

In politics, like many other spheres, we tend to valorise certainty and stigmatise ambivalence. A politician who sticks to their guns (even if they’re rigid, incurious and dogmatic) will fare better than one who vacillates (even if they’re honest, open-minded and justifiably cautious). “This is why undecided voters drive us crazy,” writes Kathryn Schulz in Being Wrong: Adventures In The Margin Of Error. “They think hard about something that most of us don’t have to think about at all. What these voters represent, however, are possibilities the rest of us often foreclose: the ability to experience uncertainty about even hugely important beliefs – the ability to wonder, right up until the moment that the die is cast, if we might be wrong.” And, in some cases, the ability to admit, after the fact, that they made the wrong call.

Serviceman Mark Olive: ‘We were deliberately misled.’ Photograph: Lewis Khan/The Guardian

Mark Olive is a 30-year-old serviceman who lives in the south of England. Before the referendum was announced, he had never thought much about the EU, so he tasked himself with reading as much information as he could from all sides. “I was just getting a negative feeling about the EU, like it didn’t serve the interests of our country,” he says. The main reason that he was undecided until referendum day was the tenor of the leave campaign. “When I saw Nigel Farage and his Breaking Point poster, I thought, actually, I don’t like any of the people who want to leave the EU.”

Nonetheless, he went for leave. “I went to sleep thinking that we weren’t going to leave and in the morning I was shocked. I remember when I went to the cafe on camp, I felt very bad straight away. There are Europeans working there and it occurred to me that I hadn’t even thought about them during the campaign. All these issues started popping up. I hadn’t thought about half of them.”

Many regretters report experiencing a visceral emotional jolt when they heard the result. “From the moment I watched the results revealed live on television that night and my vote for leave played a part, I didn’t feel joy,” says “JC”, a 49-year-old former NHS worker from Manchester. “I felt dread and fear over what would unfold for our country. Then it transpired that the leave campaign backtracked on the £350m NHS ad. I knew we’d been fed BS.”

Not enough time was given to learn all the facts. I didn’t know anywhere near enough to make such a monumental decision

People are more likely to change their minds when they’re presented with new information than when they’re asked to reassess what they already knew. For the regretters, it’s often not that key facts were unavailable at the time; rather that the complexity of the issue meant they were too easily overlooked, or the leave campaign misrepresented them, or the remain camp failed to make them unignorable. While most voters, having done their democratic duty, moved on, regretters continued to weigh the evidence.

Olive has done a lot of soul-searching. He did his research, yet still feels that he missed many important factors. The experience has made him more cynical about politicians (he has since switched from Conservative to Labour) and the media. “I think a lot about how the media shaped my views,” he says. “Would I have voted differently if I’d gone about it a different way? I definitely resent the way some of the campaigning was done. I think we as a nation were deliberately misled.”

Graeme Berry, a 48-year-old carer from Livingston, Scotland, came to the leave camp via the leftwing strain of Euroscepticism known as Lexit, persuaded that the EU was “a big-business dictatorship that prevented true socialism from being implemented”. “I had misgivings from the morning the result was declared,” he says. “The most enthusiastic leavers appeared to be on the right. I thought: what have I done?” Before the referendum, Berry had emailed the EU requesting clarification of the rules on certain issues. The reply, sufficiently thorough enough to demolish the arguments that he had believed, arrived a few days too late. “I feel that, compared with the Scottish referendum, not enough time was given for ordinary people to learn all the facts. To be honest, I didn’t know anywhere near enough to make such a monumental decision.”

Some leave voters U-turned months later, based on subsequent developments and revelations. John Chalmers, 60, runs a guest house in north Lincolnshire, a region that voted leave by a 2:1 margin. Although he was aware of the economic risk, he was swayed by his friends and neighbours, the rapid influx of eastern European migrants to Lincolnshire and the promise of more money for the NHS. He is now a staunch remainer. “I think we’re aware of a lot more now than we knew during the campaign,” he says. “What to do with this new information? Do we act on it or say no, sorry, the decision’s been made? I think we should act on it.”

I’m quite comfortable with making mistakes and changing my mind. I don’t lose too much sleep over it

Paul Hartley, a 37-year-old mechanical engineer from Lancaster, describes himself as centre-left and instinctively pro-EU, but was turned around at the last minute by his father, who argued in favour of sovereignty and taking back decision-making powers. “That resonated with me,” Hartley says. “I spent weeks convincing my partner to vote remain only to spend the last few days convincing her to vote leave!” (She didn’t.)

He felt regretful as soon as he saw how the victors were framing the result. “Every time I hear a politician talking about immigration and the will of the people, that is not what I voted for at all. The leave vote has been completely hijacked by the extreme right. I thought that common sense would prevail, but that hasn’t happened.” As for his father’s sovereignty argument: “That’s a bit of a red herring. We’ve always had the power to make decisions anyway.” Still, he is sanguine about his error. “I’m quite comfortable with making mistakes and changing my mind. I think that’s important. I wish I’d voted the other way but I don’t lose too much sleep over it.”

Meanwhile, David Towne (not his real name) has literally lost sleep over his decision. A thirtysomething “moderate Conservative” who works for a non-profit in London, he describes his guilt as a kind of psychological crisis. Despite being a longstanding Eurosceptic who preferred a European Free Trade Association-style agreement, he remained open-minded but was turned off by the remain campaign. “I reverted back to my gut feeling, because there was a lot of shit-throwing and smearing,” he says. “I don’t think the remainers I knew were looking to convert anyone to their cause. It was just: let’s denounce you all as Ukippers and racists. This caricature of the angry, immigrant-hating leaver doesn’t ring true for me at all.”

He was “shocked and panicked” by the result. “Nobody in London was happy about it, and it suddenly dawned on me that I’d voted against the interests of my city.” It was a dark time. “I was taking too much responsibility on myself. In retrospect, I’ve realised it’s disproportionate and others are far more responsible. I am just one tiny dot in the electorate. But I just felt totally fucked. I’d done something to harm my country, which I love.”

The gravity of the decision to switch from leave to remain means that regretters tend to take a hard line on Brexit. When I presented them with various scenarios, some chose a second referendum, but others wanted the process stopped in its tracks. “If I could wave a magic wand,” Olive says, “I wouldn’t want us to leave at all, because I honestly don’t think it would do anyone any good.” Towne agrees: “I’d love to call the whole thing off. It’s been head-in-hands awful, watching the lack of vision and Theresa May’s ridiculous culture war soundbites.”

Most people I spoke to felt that holding a referendum to decide policy, rather than to gauge public opinion, had been a disastrous decision in the first place. “They should have measured feelings so they could go back and negotiate,” Chalmers says. “A company doesn’t run that way. You’d need a quorum to make a decision like that.”

Hartley has been disturbed by the surge in aggressive behaviour towards people in Lancaster who aren’t white and British, including some friends from Lithuania. “It’s almost like it’s now OK to be racist. People aren’t afraid to show those feelings. Even if for some reason we don’t leave, I worry about the impact on the country.”

“For me, leaving the EU has cast a huge cloud of gloom and anxiety,” JC says. “The Tories put this mess in the hands of the British public, and for that I will never forgive them.”

***

Anyone who follows the Brexit debate via the news, Facebook or Twitter could be forgiven for thinking that both sides are inflamed with righteous passion. But Rosamund Shaw has encountered complacency and detachment among her leave-voting friends. “They won’t talk about it,” she says. “They have this Pollyanna attitude: it’ll be fine. I can’t decide if they’re being ostrich-like or if they believe it.”

Olive has also encountered a reluctance to discuss Brexit. “A lot of people who voted leave are very casual about it. They don’t think about it that much. The feeling I get is people have their minds made up, and they want to be left alone to move on to other things.”

For most Britons, Brexit is a phoney war that barely touches their lives. “From a personal point of view, things haven’t changed, so there’s no reason for them to change their minds,” YouGov’s Twyman says. “It’s like Vietnam during the Kennedy years. It’s this thing that you watch on TV but you think doesn’t affect you, and it won’t affect you until it’s your son getting the draft papers. I’ve been doing this job for 17 years and I’m never surprised by the lack of attention that most people pay to politics. We know that a lot of people voted to leave the EU so they wouldn’t have to discuss Brexit again, little knowing that we’re going to have to do nothing but that.”

People change their minds when something shakes them out of their resistance. Things will have to go badly wrong

Individually, regretters are powerless. In sufficient numbers, however, they could be extremely influential. Even when 64% of voters in YouGov’s latest poll think the negotiations are going badly, Brexiteers can shoot down criticisms by invoking “the will of the people”. But what happens to their mandate, and the perceived validity of a second referendum, if the will of the people shifts decisively and MPs begin to fear for their seats?

“The mainstream media is slanted towards leave,” Berry says. “There is no recognition of people changing their minds. I have been very active on social media to spread the truth about the EU and what we will lose. I have been accepted by the remain side. I have also made friends on the leave side, with those willing to listen. Many have changed their opinion, too.”

“It bothers me that remain politicians and public figures aren’t talking to regretters,” Towne says. “If you want to stop or dilute this thing, then you should be appealing to us. My friends and family who voted leave can all see it’s a shitshow, and we all wish we hadn’t voted for it. I’m talking about dozens of people. I think there are a lot of shy regretters who don’t show up in the polls. I think if the polls start to switch, then slowly but surely the discourse will change.”

Green says it would take a seismic event significantly to move the needle. She cites Britain’s ugly exit from the Exchange Rate Mechanism (ERM) in 1992, which hammered the Conservatives’ reputation for economic competence. “People change their minds when something shakes them out of their resistance,” she says. “Symbolic events that are so politically salient that you have to adjust your opinion. I think with Brexit things will have to go badly wrong. Something that you can’t rationalise away.”

Twyman expects to see serious movement only when a final deal is presented to the public. “Seventy per cent of people believe that in theory we should leave the EU,” he says, citing a recent poll in which only 32% actively wanted to thwart Brexit. “But what if that’s 10 groups of 7% or 20 groups of 3.5%, each group with its own particular requirements? And what if the deal that’s struck appeals to only one of those groups? There’s huge potential for change.”

Until that happens, a straight leave/remain binary won’t reflect the more subtle changes unfolding beneath the surface. “I think people can see that it’s not going well, but is that enough for them to say they would have voted in a different direction?” Green says. “I don’t think it is just yet. People are more likely to say they don’t know than they are to switch sides. That’s the destination for a lot of people who have reservations.”

Far from being a dead zone of apathy, the category of Don’t Know – ranging from 10% to 15% in polls – may therefore contain some of Britain’s most thoughtful, self-questioning voters. Chalmers proposes that we think differently about the value of changing our minds and view regret as a virtue, rather than a vice.

“I don’t feel like you have to be weak,” he says briskly. “You can apologise, pick up the pieces and make yourself stronger out of it. If you’ve made a mistake, realise it, undo it and move on. Not everybody can do that.”

• Some names have been changed.

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