Northern Ireland’s Stormont assembly faces collapse “forever” because of Democratic Unionist tactics, a rival party leader has warned. Only two years after power sharing was restored following a three-year hiatus, Doug Beattie, the leader of the Ulster Unionist party, said the DUP’s decision to resign from the first minister role 10 days ago, combined with its veiled threats not to return to power sharing unless the UK government meets its Brexit protocol demands, is putting democratic institutions at risk. Northern Ireland faces one of its most transformative elections on 5 May, with opinion polls projecting Sinn Féin will overtake the DUP as the largest party in Stormont. Beattie fears the DUP is signalling it will refuse to share power if it is returned as the second-largest party, and is using the protocol as an early excuse. This is despite the party knowing “the protocol will still be there” after the elections, because the Conservatives have made clear it is not being scrapped. “Stormont will be gone if Sinn Féin come back as the largest party and the DUP second. It will be gone forever,” said Beattie. “The UK government and Northern Ireland Office are being dragged around by the scruff of the neck by the DUP. “They are creating divisive politics and until somebody stands up to them and says ‘no, you can’t do this’, it’s not going to end well. And that’s what’s happening here,” he adds. The Northern Ireland secretary, Brandon Lewis, said all unionists parties should give a commitment they would nominate ministers in the event of Sinn Féin becoming the largest party after the next election. The UUP has refused to give a public commitment, but is unlikely to be in a position to take the deputy role. Beattie’s party is on 14% in the polls, in joint third position with the Alliance party, while the DUP stands at 17%. The DUP has repeatedly refused to say whether it would accept the office of deputy first minister, a sign of things to come if Sinn Féin is victoriious, critics believe. Legally, under the Good Friday agreement the deputy first minister role is equal to first minister with parties sharing power at the top equally. Last week, the DUP leader, Sir Jeffrey Donaldson, gave the electorate another glimpse of its strategy, warning it would be “difficult” to return to Stormont if the protocol was not resolved by the elections, remarks that horrified rivals. Speaking from his offices in Portadown, Beattie accused Boris Johnson of being part of what he believes is naked electioneering. “The UK government had the opportunity to legislate to make the first minister and deputy minister equal in name. They chose not to. They are both gambling with Northern Ireland. It is beyond reckless,” he said. Beattie has cast his party as more liberal and progressive than his rivals, but is as opposed to the protocol as the DUP. However, Beattie believes his party respects democracy. He said: “The difference between us and the DUP is we’re not willing to collapse institutions to do something that we can do through dialogue and engagement and speaking to people.” The UUP has presented the Tories and the EU with a five-point blueprint to fix the protocol. It includes the elimination of all checks on goods from Great Britain destined to stay in Northern Ireland through a self-certification process, a new law enabling fines for any company in GB that certified goods to NI but sent them on to the Republic, and a legal indemnity for the EU against cross-border breaches of the new protocol. It also wants to see Stormont’s four-year rolling vote on keeping or ditching the protocol scrapped, as well as tackling the role of the European court of justice and the “democratic deficit” that leaves Northern Ireland with no say on potential new laws coming out of the EU. However, Beattie does not trust Johnson’s repeated promises to deliver on fixing the protocol. “I do not trust him a jot. He’s all rhetoric and soundbites. I don’t dislike him personally, but he is just not connected. I don’t think he’s a good prime minister,” said Beattie. He said he had faith in Liz Truss, the foreign secretary, but asked “what on earth was Johnson doing giving her the Brexit role?” when she had to deal with Ukraine and China. The DUP was approached for comment. • This article was amended on 14 February 2022. Power sharing was restored two years ago, not one as stated in an earlier version.