Sinn Féin has appealed to the UK government to bypass the Northern Ireland assembly and introduce Irish-language legislation via Westminster to defuse a political crisis that threatens to collapse Northern Ireland’s power-sharing government. Conor Murphy, the Sinn Féin finance minister, said on Tuesday that the party would end a standoff over rebooting the stalled Stormont executive if London delivered the legislation. Some unionist leaders condemned the proposal as an attempt to bypass devolved government and urged the British government to not get involved. The spectacle of Sinn Féin appealing to Boris Johnson, a Conservative prime minister, and unionists saying it was none of his business, was the latest twist in a crisis involving the Irish language, the Irish Sea border, Democratic Unionist party (DUP) turmoil and the loyalist marching season. Following an internal DUP revolt, Arlene Foster resigned as first minister on Monday. Under Stormont rules the deputy first minister, Sinn Féin’s Michelle O’Neill, also had to step down. The DUP’s new leader, Edwin Poots, has chosen a party ally, Paul Givan, to take over as first minister. However, Givan cannot be ratified unless Sinn Féin renominates O’Neill, which it says will not happen without the long-promised Irish-language legislation. If the stalemate is not resolved by 21 June, the devolved power-sharing institutions will collapse and there will be an early assembly election, with no guarantee of any subsequent agreement to revive Stormont. Murphy, Sinn Féin’s chief negotiator, told RTÉ that Sinn Féin would “move ahead” to end the impasse if Irish-language legislation was delivered. “This isn’t about a Sinn Féin demand. This is an agreement we all reached. We have already told the DUP they need to deliver on this. We have exhausted the conversation with the DUP. This isn’t about issuing ultimatums, this is about trying to find agreements.” Murphy repeated an earlier assertion by Sinn Féin’s leader, Mary Lou McDonald, that the British government several weeks ago offered to pass such legislation, an offer the party said it initially rebuffed in expectation of a deal at Stormont. The SDLP leader and Foyle MP, Colum Eastwood, said he would seek to table amendments to legislation at Westminster. The second reading of the Northern Ireland (ministers, elections and petitions of concern) bill is scheduled on 22 June. Julian Smith, the former Northern Ireland secretary of state, said he would support such an initiative. The Alliance party leader, Naomi Long, said intervention by Westminster could be a “partial solution” to a crisis that could dissolve the assembly just 17 months after it was revived. The legislation was promised in a 2020 deal that revived Stormont three years after its collapse over other disputes. Sinn Féin says such legislation will show respect and equality for Irish culture. Many unionists say nationalists have “weaponised” the language to undermine the region’s sense of Britishness. Jim Allister, the leader of the Traditional Unionist Voice party, said some in the DUP might privately welcome Westminster’s intervention to resolve the crisis and avert an election, but that such intervention would kill Stormont. “If devolution can be bypassed by republicans at will, then there is no point in devolution,” he said. Sammy Wilson, a DUP MP, urged Downing Street to stay out of the row. “The government foisted the most liberal abortion laws in the British Isles on Northern Ireland. Such actions only served to undermine devolution. To force through the latest Sinn Féin wishlist will cause further damage to the credibility of the Northern Ireland assembly.