The decision to quit the EU bolstered support for Scottish independence, which a decade after the Brexit referendum is at near record levels, according to Scottish Labour’s former leader Kezia Dugdale.

Dugdale said the Brexit vote “creates a frame around fairness” for many in Scotland because, unlike England, Scottish voters comprehensively backed remain in 2016, by 62% to 38%, yet found their country taken out of Europe.

She also believed the UK government’s embrace of a “hard Brexit” swayed many Scots who had been undecided about Scottish independence when a referendum was held on the issue in 2014.

Support for independence currently stands at about 50%, reaching 55% in some polls.

Dugdale recalled feeling “utterly devastated” when the leave result was confirmed early on 24 June 2016. That morning, she spoke privately to the then first minister, Nicola Sturgeon, telling her: “This changes everything.”

She said many Scots felt they “faced an immediate binary choice of an independent Scotland in Europe or a Boris Johnson-led Brexit Britain”, and that sense of betrayal changed the landscape of Scottish politics.

“I think it sustained support for independence, which otherwise would have fallen back,” she said.

Ruth Davidson, who was the Scottish Conservative leader in 2016 and championed the remain campaign, was shocked by the leave result.

She recalled speaking that day to Sturgeon, who sought to persuade her to “move forward together” alongside Dugdale in support of a second independence vote. “I can remember thinking ‘no, no, no’,” Davidson said. “The remain vote shouldn’t be coopted for something it wasn’t for.”

In her memoir Frankly, Sturgeon said:“I felt distraught and enraged by the prospect of Brexit and what it said about Scotland’s powerlessness within the UK. I had a strong sense of ‘If not now, when?’”

There was speculation that in the wake of Brexit, support for Scottish independence could surpass 60%, but the tidal wave many expected did not transpire.

Instead, over the past decade, the issue’s salience faded as the political crises that followed Boris Johnson’s hard Brexit, the Covid pandemic, the Ukraine war, and Donald Trump’s chaotic presidencies translated into deep insecurity about the economy and public services.

Davidson, a staunch unionist, said she retained her “animosity” towards Johnson, who she believes neglected to show genuine leadership and failed to articulate a coherent vision for a unified post-Brexit Britain. But the “Boris effect” on support for independence was much less significant than she had feared.

“There was a hierarchy of concern” for voters, she said. “Whether we were for independence or for staying in the UK was a more material concern than the UK’s relationship with the EU.”

The electoral realities of that tension could be seen as early as 2017.

Sturgeon’s attempts to leverage remainer anger into an irresistible case for a second referendum floundered. Theresa May’s Conservative government resisted her demands. Support for independence fell during 2017 to below 40%.

In the 2017 general election, the SNP lost 21 Westminster seats and its vote share fell 13 points as voters punished Sturgeon for demanding a second independence vote. The pro-UK parties, which had previously held only a seat each, enjoyed a renaissance.

Davidson’s Tories won 13 seats; Dugdale’s Labour won seven, and the Lib Dems four. In the five UK and Holyrood elections since, the SNP has never won 50% of the vote, weakening its claims to a mandate for a second independence referendum.

Yet during 2019, with Johnson succeeding May as prime minister and pressing forward with a hard Brexit, followed by his blundering failures during the Covid crisis in 2020, independence polling changed.

As Sturgeon became a commanding presence in contrast to Johnson’s chaotic leadership, support for Scotland leaving the UK surged, reaching 59% by October 2020.

Economic decline and fears about the NHS now dominate the Scottish political agenda. Dugdale traces much of that to Brexit, and its impact on the UK’s economy.

Based on recent estimates from the National Institute of Economic and Social Research, the Scottish government’s Europe minister, Stephen Gethins, told Holyrood on 18 June that Brexit led to £3.3bn in lost revenue for Scotland last year and added £250 to food bills.

Prof Mairi Spowage, the director of the Fraser of Allander Institute, a leading Scottish economics thinktank, argued that while it was clear Brexit had hit economic output, EU exports and public finances, its precise impacts had been obscured by other crises and policy failures.

She said the UK’s economic decline could be partly traced to longer-term underinvestment by business and government since the 2008 banking crisis. Since then, Covid, Ukraine, the Liz Truss government, US trade policy and wars in the Middle East have also affected the economy.

Migration to the UK, too, has been complex: the “Boris wave” of post-Brexit migration has offset a fall in EU workers – partly due to increasing prosperity for EU member states, once a source of migrant labour.

Despite the efforts by John Swinney, the first minister and SNP leader, to make Scottish independence and rejoining the EU central to the recent Holyrood elections, that gambit failed to deliver the overall majority he craved.

The SNP achieved 38% of the vote, its lowest since 2007, and won most seats only because the opposition was divided. The anti-EU party Reform UK drove that opposition split, winning 17 seats and is now jointly Holyrood’s second largest party; some of its voters were EU sceptics who once backed the SNP.

Dugdale, now an associate director of the Centre for Public Policy at Glasgow University, is no longer a member of the Labour party and voted SNP in the last European parliament election in 2019 in protest over Brexit.

Many voters are now driven by anger and disillusionment, partly because of a belief that Brexit failed to deliver on its supporters’ promises. “We’ve had more than 15 years of austerity and 15 years of falling trust in political institutions,” Dugdale said. “If we sustain these things long enough, people no longer trust the system to make their lives better.”