Keir Starmer has promised Scottish National party voters that Labour will shift power from London and “fix” Brexit, as he sought to capitalise on Nicola Sturgeon’s departure. The Labour leader made a direct appeal to Scottish voters, telling them he understood why some were disillusioned with the UK and acknowledged that SNP supporters had a fair case. “Those Scots who lost faith in Britain, they have a point about Westminster,” Starmer told Scottish Labour’s spring conference in Edinburgh on Sunday. “Britain has an economy that hoards potential and a politics which hoards power, and these two problems feed off each other. “I’m utterly convinced about this – economic reform and political change must go hand in hand.” Starmer delivered his speech five days after Sturgeon stunned her party and most Scottish voters by unexpectedly announcing that she was standing down as first minister and as SNP leader. On Sunday, the health secretary, Humza Yousaf, and the former community safety minister Ash Regan confirmed that they would stand in the party’s leadership contest, with at least a further two candidates – Angus Robertson, the culture secretary, and Kate Forbes, the finance secretary – also expected to declare in the next 48 hours. Mairi McAllan, the environment minister, ruled herself out on Sunday, saying now was “not the right time” for her to compete in the leadership race. “I believe it is vital that progressive voices, including those of women and young people, are central to our party, our government and to the Scotland we are seeking to build. Our voices matter and they must be heard,” she said on Twitter. In competing interviews with the Sunday Mail newspaper, Yousaf and Regan immediately opened up deep divisions on the two biggest political challenges facing the SNP, on how to achieve independence and on gender recognition. Regan made an appeal to traditionalist SNP members by stating she would work with Alex Salmond’s hardline Alba breakaway party on independence. Regan, who quit Sturgeon’s government in protest at her gender recognition proposals, said she would scrap the first minister’s reform bill. Yousaf, rumoured to be Sturgeon’s preferred candidate, said more time was needed to devise a fresh approach to independence. He said the Scottish government should fight the UK government’s decision to block the gender recognition bill in court, in part to defend Holyrood’s autonomy. In a reference to Labour’s pledge to abolish the House of Lords and increase the powers and independence of the Scottish and Welsh parliaments, Starmer told delegates: “A huge power shift out of Westminster can transform our economy, our politics and our democracy.” That stance, which echoes Labour’s attempt to win back leave voters in “red wall” seats by promising more powers for northern England, is an effort to appropriate the SNP’s central line of attack on the UK – that Westminster suffocates Scottish aspirations. At the same time, he said, “we will also seek to reset relations with the European Union. We will look to increase trade, reduce frictions, fix the Brexit deal. It’s a key part of raising our ambitions on economic growth.” Starmer offered little detail on his post-Brexit strategy with the EU, underlining a dilemma for Labour in Scotland, which the SNP will continue to exploit. A large majority of Scots favour rejoining the EU while Labour believes red wall voters would revolt if it tried to reverse Brexit. Labour’s leaders are privately delighted Sturgeon has quit, believing it offers them a huge opportunity to regain lost ground in Scotland, where it has only one MP, in the next general election. The party anticipates political and ideological conflicts between the competitors to replace Sturgeon that they believe should undermine public confidence in the SNP after 15 years of political dominance. Starmer told delegates “the energy and buzz about this conference is phenomenal”, but warned them against complacency. He said the “brutally honest” truth was that Sturgeon had won and maintained her majorities by persuading Labour voters to defect to the SNP. Labour, he said, had to prove it was worth voting for. “We won’t change any hearts or minds by sitting back and watching a battle for power within the SNP,” he said. “Or by assuming that any weakening of faith in their case automatically benefits us. We have to go out there and earn it.”