Northern Ireland is on course for a snap election after a recall of the Stormont assembly failed to elect a speaker and break political deadlock. The Democratic Unionist party (DUP) blocked an attempt to revive the assembly and executive on Thursday, perpetuating paralysis and running down the clock to a midnight deadline to restore devolved government. The party rebuffed appeals from the prime minister, Rishi Sunak, business leaders and other parties, saying it had a mandate from its supporters to boycott Stormont unless unionist objections to the post-Brexit Irish Sea border were resolved. If power sharing is not revived before Friday, by law, caretaker ministers must step down to be replaced by civil servants, and there must be an assembly election within 12 weeks. Assembly members traded blame over why an assembly election last May had produced seven months of stalemate and the prospect of another poll, probably in December. Michelle O’Neill, Sinn Féin’s vice-president, said people were “bewildered” and accused the DUP leader, Jeffrey Donaldson, of blocking democracy. “This is his mess, and a failure of leadership by him and his party.” Naomi Long, the Alliance party leader, said politicians were placing party interests over those of a region where public services were “on their knees”. The Ulster Unionist party (UUP) leader, Doug Beattie, said anger in the chamber was nothing compared with what voters were feeling, adding: “I guess we are all going to feel that anger in the next six or seven weeks.” Matthew O’Toole, the Stormont leader of the Social Democratic and Labour party (SDLP), said another election would be a farce. “My party is not responsible for that mess but I’m ashamed by it.” The assembly recall – requested by Sinn Féin and Alliance – followed inconclusive talks on Wednesday between the Northern Ireland secretary, Chris Heaton-Harris, and party leaders, including Donaldson. The DUP leader remained defiant despite a Downing Street spokesperson swelling the clamour for the party to restore power sharing. “We do not believe that sufficient progress has been made,” said Donaldson, referring to the Irish Sea border. His party had a mandate to block the appointment of an assembly speaker – a prerequisite to form an executive – without “decisive action” on the Northern Ireland protocol, he said. The UK government had hoped the spectre of an election would compel the DUP to end its boycott but the party does not fear a poll. Its unyielding stance has proven popular with supporters. Sinn Féin seems equally confident of matching or exceeding its result in May, when it became the largest party, a landmark result that made O’Neill the putative first minister. Such outcomes would squeeze the more moderate UUP and SDLP, while Alliance would be expected to win support from people fed up with Stormont’s endless crises. The assembly has not functioned for four of the past six years, leaving civil servants to run government departments and public services in a form of autopilot. Business leaders said the political vacuum was deterring investment and costing jobs. Nationalist parties and the Irish government said that in the absence of devolved government, Dublin should have a greater role in Northern Ireland, working in partnership with London. Unionists rejected any form of “joint authority” as unacceptable. The latest impasse has deepened a sense of political malaise in Northern Ireland and raised questions about the viability of power-sharing institutions established by the 1998 Good Friday agreement. Beattie, the UUP leader, expressed fear that the assembly “will never be back”.