The Northern Ireland secretary has announced he will call an election for the Stormont assembly but refused to name a date. Chris Heaton-Harris said on Friday he would do his “legal duty” to call an election within 12 weeks and promised to give more detail next week after talks with Northern Ireland party leaders. The statement, made at a hastily organised press conference in Belfast, caused confusion and left open the possibility the UK government would try to delay the poll. A deadline to restore devolved government expired at midnight on Thursday, which by law means there must be an election for a new assembly within 12 weeks. Heaton-Harris had vowed to swiftly announce one if the deadline expired, creating expectations of a mid-December poll. However, in a rare consensus, Northern Ireland politicians and analysts had said an election would be futile and do nothing to break a political deadlock that has paralysed Stormont. In a brief address to the media, Heaton-Harris sought to buy more time. “I hear when parties say that they really do not want an election at all but nearly all of them are parties that signed up to the rules, to the law, that means I need to call an election,” he said. “So you’ll hear more from me on that particular point next week.” The Northern Ireland Office said the statement, given to TV cameras on a pavement in view of the public at 4pm, was to be embargoed until 5pm, a request that was widely mocked and created a sense of disarray in the Northern Ireland Office. Heaton-Harris denied making a U-turn. “I am still going to be calling an election,” he said. He linked the pause in naming a date to negotiations between the UK and EU over the Northern Ireland protocol. “The atmosphere in those talks is completely changed in recent weeks and I am optimistic and I really do believe that we can get somewhere on those too,” Heaton-Harris said. Northern Ireland’s chief electoral officer, Virginia McVea, said she would continue making a contingency plan for a 15 December election and apologised to election workers for the uncertainty. The Democratic Unionist party created the deadlock after an assembly election in May by boycotting power sharing in protest against the post-Brexit Irish Sea border. This prevented the formation of an executive, leading to seven months of political stasis. The party’s leader, Jeffrey Donaldson, rebuffed appeals from Downing Street, business leaders and other parties to revive power sharing, saying he had a mandate from DUP voters to stay out of Stormont until unionist concerns over the Northern Ireland protocol were addressed. After Heaton-Harris’s statement on Friday, Donaldson accused the secretary of state of dithering. “The chaos continues,” he said. Michelle O’Neill, Sinn Féin’s vice-president, said it was a “bizarre U-turn”. “People here are left in limbo and uncertain what is to come next,” she said. Heaton-Harris had raised the spectre of an election to pressure the DUP but the party dug in, saying it did not fear a poll, and vowed to continue its boycott after an election if the protocol remained unchanged. The former taoiseach Bertie Ahern swelled a clamour saying an election would be futile. “It doesn’t matter whether people vote black, white, yellow or pink in the election, it won’t change anything. The protocol is still the protocol and it isn’t up for discussion in the election,” he told RTÉ. Jon Tonge, a politics professor at the University of Liverpool and an authority on Northern Ireland elections, said Heaton-Harris was wavering: “He’s now playing for time hoping something will turn up.” Tonge urged the government to pass emergency legislation to postpone the vote and overhaul power-sharing rules so that no party could veto an executive. The assembly has not functioned for four of the past six years, leaving civil servants to run government departments and public services. Business leaders said the political limbo was deterring investment and costing jobs.