As Ireland, north and south, grappled with Boris Johnson’s reported threat to renege on the Brexit withdrawal agreement, there was consternation, anxiety, dread – and the hope that it is a bluff. In Dublin, the Irish government attempted to project a sense of concern rather than panic while in Belfast political parties sounded the alarm over the revived prospect of a hard border between Northern Ireland and the Irish Republic. All sides – diplomats and politicians, nationalists and unionists – tried to determine whether Downing Street was posturing or serious about unpicking legally binding special arrangements for Northern Ireland. Simon Coveney, Ireland’s foreign minister, said media reports that London was planning legislation to override parts of the withdrawal agreement would, if confirmed, damage 11th-hour trade talks with the EU. “It would fundamentally undermine trust between the two parties,” he told RTE. Coveney said Dublin did not know if the threat, first reported by the FT, was a false report, political gamesmanship or a real prospect. “We’ll have to wait and see.” There is grave concern in Dublin that a hard border on the island of Ireland and severe economic disruption from a no-deal Brexit – its nightmare scenario – will materialise. Coveney’s earlier warning that unravelling the withdrawal agreement would be “unwise” showed mastery of the supposedly British art of understatement, said Bobby McDonagh, a former Irish ambassador. The taoiseach, Micheál Martin, is to unveil an updated Brexit readiness plan on Wednesday amid a dire economic backdrop and Covid-19 resurgence. Billy Kelleher, an MEP from the ruling Fianna Fáil party, said he initially dismissed rumours that Britain may bypass the Northern Ireland protocol as a “wind-up” given its impact on Britain’s credibility. “This is an incredibly worrying time for Ireland, the rest of the EU and indeed the UK. No good can come from this level of brinkmanship. People’s livelihoods are being bartered away by the Tories in a way reminiscent of the 18th or 19th century and not of the modern era.” Kelleher said he believed the threat was a ploy and urged Michel Barnier, the EU’s chief negotiator, to stand firm. In Northern Ireland, nationalist parties warned that rowing back on legally binding commitments would undermine the 1998 Good Friday agreement and destabilise the region. “The impact will be negative, and the only safeguards we have to mitigate the damage is the protocol,” said Michelle O’Neill, the deputy first minister and Sinn Féin’s deputy leader. “This would be a betrayal of what has already been agreed and would inflict irreversible harm on our economy and the Good Friday agreement.” O’Neill said Sinn Féin would seek to rally support in Northern Ireland’s Stormont assembly as well as Dublin, Brussels and Washington to defend the “foundation stones” of the peace process. Colum Eastwood, leader of the Social Democratic and Labour party, said it was astonishing and reckless that the British government would shred its own credibility and undermine the Good Friday agreement. “They’d be risking a hard border in our country and they’d be threatening the peace and security that we’ve built up over decades,” he told the BBC. “If they try to do this at the same time as trying to convince people in Scotland and Northern Ireland about the future of their union, well they may as well forget about that as well.” The Alliance party also voiced concern at potential damage to the Good Friday agreement. The Democratic Unionist party (DUP), which opposed special arrangements for Northern Ireland, made no immediate official response. On Friday its leader, Arlene Foster, said she recognised the protocol was law and that the challenge was to mitigate its impact, only to have the rug pulled from under her by Downing Street’s announcement. Sammy Wilson, the DUP’s Brexit spokesperson, said the party would not accept the withdrawal agreement – a flat contradiction of his leader that was not issued through the party’s press office.