The UK government’s plan to walk away from parts of the Northern Ireland Brexit deal is destroying the repaired relationship with the EU, political leaders and diplomats have said. Leo Varadkar, Ireland’s deputy prime minister, told a business dinner in Dublin on Tuesday night that the move was “breeding mistrust in EU capitals”. A measure of the anger and disbelief within the EU was reflected in a tweet posted by the German diplomat Sebastian Fischer, considered one of the most mild-mannered of his cadre in Brussels. “Let’s just all threaten each other with breaking international law. Makes for really good partnerships #Brexit,” he tweeted on Tuesday evening. “If you are wondering what friends and allies think …” tweeted Ireland’s foreign minister, Simon Coveney, in response. There is a growing feeling of disbelief and disappointment in the EU over the UK’s position, given the goodwill that the prime minister, Boris Johnson, had built up over Ukraine. One EU diplomat said unilateral action was “neither necessary nor desirable”, adding that the timing could not be worse. “One would imagine that the foreign secretary [of the UK, Liz Truss,] to be well placed to assess the geostrategic implications of her actions, but she seems to prioritise domestic politics over peace and stability on the European continent,” the source said. “The fact that the UK government is talking openly about breaching international law is a matter of concern,” Varadkar said. “[It] stands in contrast with the enormous leadership the UK government is showing in supporting Ukraine against Russia, which has breached international law in a very serious way,” the tánaiste said. He co-designed the protocol with Johnson in October 2019 to deliver a breakthrough that helped the Conservative party leader present what he described as an “oven-ready” real to the electorate in an election the following December. There are fears that the relationship between London and Brussels, which had deteriorated badly over the past four or five years due to Brexit, has once again been damaged. EU negotiators are said to be frustrated at what they see as the UK government’s failure to engage with proposals to reform the Northern Irish protocol laid out by the European Commission vice-president Maroš Šefčovič last autumn. Sources believe the proposals have the potential to solve many problems raised by businesses in Northern Ireland. The government’s aim of waiving all checks on goods travelling from Great Britain to Northern Ireland that are not destined for the Republic of Ireland, is seen as a reversion to earlier unsolved Brexit debates. “We are back to issues that it was not possible to square in 2017,” said one diplomat, who added there was a “lack of honesty” about how the UK government’s chosen hard Brexit had created checks and red tape. “The more Great Britain wants to diverge from the EU the more difficult [the issue of] Northern Ireland becomes.” But one EU source said they had expected the move and believe Johnson will ultimately pull back from any attempt to break a treaty signed two years ago. “There will be American pressure on Boris Johnson. The US will not want to see a rift in Europe at this time. It simply will not allow a trade war,” they said. Speaking in Dublin on Tuesday, Coveney said there had been “no serious engagement since February” between the EU and the UK, contrary to claims by Truss in the Commons that she had been engaged in talks for the past six months.