Nicola Sturgeon has resigned as Scotland’s first minister in a surprise decision that has thrown the Scottish National party into turmoil, triggering its first leadership contest in nearly 20 years. In a hastily arranged press conference in Edinburgh, Sturgeon said she no longer had the stamina to continue in the highly pressured and demanding role. She said “in my head and in my heart” she believed this was the right time for her to quit and build a new career outside politics, after eight years as Scotland’s longest-serving first minister and as the first woman to hold the post. “A first minister is never off duty. Particularly in this day and age, there is virtually no privacy. Ordinary stuff that most people take for granted, like going for a coffee with friends or for a walk on your own, becomes very difficult,” she said. “And the nature and form of modern political discourse means there is a much greater intensity – dare I say it, brutality – to life as a politician than in years gone by. All in all, it takes its toll on you and on those around you.” She said the SNP’s national executive had been asked to begin the process of electing a new leader and would remain in office until her successor is chosen. It last fought a leadership election in 2004, when Sturgeon ran as Alex Salmond’s running mate. Her resignation, which many had suspected could happen nearer the next Holyrood election in 2026, triggered speculation about her successor and also opens up the prospect of a significant Labour revival in Scotland. Bookmakers quickly tipped Angus Robertson, the SNP’s former Westminster leader and now Sturgeon’s cabinet secretary for culture and external affairs, as the lead candidate but there remains no clear successor to Sturgeon. She was anointed party leader in 2014 without a contest after Salmond resigned; this time little attention has been paid to succession planning within the party. Labour sources believe her resignation has given them an unexpected opportunity to win back up to 15 or 20 seats at the next general election, boosting their chances of securing an overall UK-wide majority. Bolstered by Labour voters supporting yes in the 2014 independence referendum, Sturgeon had been highly skilled at attracting Labour voters to the SNP, by pulling her party firmly to the left and making the SNP the flag bearers for Scotland’s anti-Tory vote. With Scottish Labour hosting its spring conference in Edinburgh this weekend, its strategists believe it is highly unlikely her successor will have the skills or appeal to replicate that at the next election, allowing it to regain lost ground. “This puts 14, 15, 16 seats up for grabs,” said one candidate. A Scottish business leader with links to the party was even more bullish. “It should now be 15+, and maybe as high as 25,” they said. The SNP leader has had a series of political setbacks recently, including the UK supreme court defeat of her plans for a fresh independence referendum and a damaging row over double rapist Isla Bryson being sent to a female jail after announcing she was a trans woman. Sturgeon told reporters at Bute House, her official residence in Edinburgh, that she had felt for some months that her energy and desire to remain as first minister was wavering. That feeling had solidified in early January and had grown since, she added. “I have spent almost three decades in frontline politics, a decade and a half on the top or second-top rung of government,” she said. “So if this was just a question of my ability or my resilience to get through the latest period of pressure I wouldn’t be standing here today, but it’s not. This decision comes from a deeper and longer-term assessment. I know it may seem sudden, but I have been wrestling with it, albeit with oscillating levels of intensity, for some weeks.” She said she had decided to quit now because the SNP was holding a special one-day conference in mid-March to debate how best to seek a fresh independence referendum, after the supreme court rejected her claim that Holyrood had the power to legislate for another vote without Westminster approval. One Holyrood source suggested the party may now turn that event into a leadership hustings or change the agenda, to avoid Sturgeon’s successor being tied into a policy he or she has not defined or controlled. Sturgeon said she knew she did not have the energy to commit to that cause for as long as necessary. The SNP needed to know that a new leader would have to take up that quest before deciding on its independence strategy, she added. Her resignation also reignited speculation about a Police Scotland investigation into the fate of £600,000 in donations to the SNP given to mount its next independence campaign, and the decision by her husband, Peter Murrell, the SNP chief executive, to lend the party £107,000. The police are consulting with senior prosecutors at the Crown Office, but the SNP has insisted there was no wrongdoing. Sturgeon’s opponents suspect that inquiry could prove extremely embarrassing to the party. Joanna Cherry KC, a senior SNP MP and leading critic of many of Sturgeon’s policies, tweeted that Murrell should now resign and be replaced by a “neutral” caretaker chief executive. “The SNP leadership and party management have been deeply bound together,” she said. Sturgeon also indicated she may not stand again for Holyrood in 2026, saying she would remain as an MSP for the remainder of her current term and make a final decision on defending her seat of Glasgow Southside closer to the election. There had been growing speculation that Sturgeon was preparing to stand down at the next Scottish parliamentary election, but not so abruptly. She had repeatedly told reporters she had no plans to quit and intended to lead the Scottish government and SNP into the Holyrood elections in 2026. Yet a series of opinion polls have shown popular support for Sturgeon personally and for the SNP and independence has fallen in recent weeks, partly fuelled by the intense controversy over Bryson. A poll by the Sunday Times at the weekend showed 42% of voters wanted Sturgeon to immediately resign, while 45% said she should remain in post until the next Holyrood election and 13% did not know. The poll found 15% of those who voted SNP at the 2019 general election wanted her to quit, as did 19% of those who voted yes at the 2014 independence referendum. However, 76% of SNP voters and 72% of yes voters wanted her to remain. Many of her political opponents applauded her contribution to Scottish politics. Anas Sarwar, the Scottish Labour leader, said Sturgeon was due “respect and thanks” for her leadership during the Covid crisis. “While we have disagreed passionately about what is best for our people, I have never for a moment doubted her passion for Scotland,” he said. Douglas Ross, the Scottish Conservative leader, was far more critical, saying: “We cannot ignore that she has presided over a decade of division and decay in Scotland. Instead of trying to unite the country in the wake of the 2014 referendum, Nicola Sturgeon refused to accept the result. [As] a result, Scotland has been in a state of constitutional paralysis ever since.”