Rishi Sunak has ruled out any further devolution of powers for Scotland after telling Conservative activists that Holyrood should be “held to account” more for underusing its existing powers. The prime minister claimed Holyrood already had significant powers, including over income tax rates, telling delegates at the Scottish Conservatives’ annual conference in Glasgow there was therefore no case for adding to them. “Scotland already is the most powerful devolved assembly anywhere in the world,” he said during a question-and-answer session chaired by Douglas Ross, the Scottish Tory leader. “The SNP and the Scottish government doesn’t even use the powers they already have, so we shouldn’t start talking about any more. What we need to do is hold them to account.” His remarks suggest there will be an intense contest between Labour and the Conservatives over Scotland’s powers at the next general election, which could further divide the anti-independence vote in Scotland. Keir Starmer, the UK Labour leader, has committed his party to sweeping changes in Britain’s political structures, including abolishing the House of Lords, and as-yet-unspecified new powers for Holyrood. He also supports Holyrood’s higher taxes for higher earners – a policy the Tories oppose. As well as reform-minded unionists, Labour hopes to attract pro-independence voters who may see enhanced devolution as a compromise solution now that the prospects of a second independence referendum have greatly subsided after Nicola Sturgeon’s resignation, the SNP’s ill-tempered succession battle and the crisis with the police investigation into SNP finances. In his conference speech later on Friday, Ross abandoned a previous proposal that Tory voters in SNP-Labour and SNP-Liberal Democrat marginals should consider voting tactically by backing the best-placed unionist party instead of automatically voting Tory. That proposal, which Ross made in an interview with the Daily Telegraph this month, was quickly shot down by No 10. Sunak’s remarks and his short speech earlier to delegates were overshadowed by a heated row involving No 10 officials and Scottish political journalists after Downing Street tried to restrict access to a briefing with Sunak to six handpicked newspapers. A large group of reporters, who were accredited to cover the conference and were also members of the Scottish Parliamentary Journalists’ Association, sidestepped party officials and entered the briefing room, followed by television crews. The dispute follows a previous clash between Westminster lobby correspondents and No 10 officials who tried to restrict access to briefings with Boris Johnson to handpicked media outlets. After a protracted and at times fractious standoff in Glasgow, during which No 10 insisted that reporters and TV crews who had not been invited had to leave, and then threatened to cancel the briefing, it took place an hour late with every newspaper reporter present. In his conference-floor appearance, Sunak also said the UK government had the right to sidestep the Scottish parliament by directly funding initiatives at local level in policy areas devolved to Holyrood, as part of its levelling up agenda. The Tories argue that Scotland has two governments – at Holyrood and at Westminster – and that was “really healthy”, Sunak said, adding that it was well-received by Scottish councils and local communities. “We know that in the same way that Westminster doesn’t always know best, it’s not the case that in Scotland the SNP and the Holyrood government always know best,” he said. “We don’t have to just hand everything over to the Scottish government. I think that’s real devolution, or devolution in action at a very local level.”