The UK’s newly appointed chief post-Brexit negotiator, Liz Truss, said she would speak to her EU counterpart, Maroš Šefčovič, on Tuesday amid renewed calls to rip up the controversial Northern Ireland protocol. The cabinet minister, who is also the foreign secretary, said she wanted to negotiate “a comprehensive solution” to the agreement, which requires post-Brexit checks on goods arriving in Northern Ireland from Great Britain. Allies added that she wanted to “hit the ground running”, but offered no further details on how she will handle the technical discussions about customs arrangements, which could have wide political ramifications. No EU-UK talks had been scheduled in the last days before Christmas, until the surprise weekend resignation of Lord Frost, who had been Boris Johnson’s chief Brexit negotiator. Ministers remain under pressure from Conservative hard Brexiters and Northern Ireland’s Democratic Unionists to resolve an issue they argue has led to the creation of a border down the Irish Sea – and damaged the integrity of the United Kingdom. Sir Jeffrey Donaldson, the DUP leader, told the BBC that he had been led to believe by Frost that the talks were struggling to progress: “He felt, I think, that we were fast approaching the time when the UK government needed to take unilateral action.” Article 16 of the protocol allows one side or the other to rip up part of the agreement – such as customs checks between Great Britain and Northern Ireland – in the event of “serious economic, societal or environmental difficulties”. But it could expose whoever acts to retaliatory tariffs. John Finucane, a Sinn Féin MP, said the British government should show “a degree of responsibility and realism” over the protocol, which allows Northern Ireland special access to the EU single market. He said the agreement provided “enormous economic benefit to this jurisdiction”. Truss supported remain during the 2016 referendum campaign, but is popular with Tory activists at a time when Johnson’s premiership is in crisis due to a string of revelations about lockdown-breaking gatherings at No 10. One hard-Brexit source on the party’s backbenches said they were supportive of Truss’s appointment, but wanted her to “focus on the detail and not just the showboating” – after she was pictured riding on a tank in Estonia last month, in a pose reminiscent of Margaret Thatcher. Truss will combine the role with her position as foreign secretary, the first time the jobs have been united since the UK voted to leave the EU in 2016. One former Downing Street insider said “both roles are so full-time” and wondered whether she can effectively focus on both. During the 2016 EU referendum campaign, Truss, speaking at a remain campaign event as environment secretary, said: “I don’t want my daughters to grow up in a world where they need a visa or permit to work in Europe, or where they are hampered from growing a business because of extortionate call costs and barriers to trade.” The minister co-authored a pamphlet with Labour’s Ed Miliband, Lib Dem leader Ed Davey and Green MP Caroline Lucas. They warned: “If Britain leaves Europe, our environment … will be starved of investment, bereft of protections and denied the leadership it needs.” Brexiters criticised it as scaremongering. Truss also agreed with Lord Frost, then president of the Scotch Whisky Association, in arguing that membership of the EU single market was critical to the successful exports of the spirit. “Europe has a taste for Scotch and the industry will do better if we remain in the EU,” she said. Allies of Truss said that the minister had made clear that she had changed her mind and would vote leave if she had the chance again. Her stint as international trade secretary, before becoming foreign secretary, had demonstrated her credentials as a free marketeer and free trader, they added.