Boris Johnson’s row with the EU over Northern Ireland’s Brexit arrangements is “absolutely solvable” but only if the UK accepts that a border is inevitable, the former head of the World Trade Organization has said. But Pascal Lamy said the prime minister could only achieve a breakthrough if he stopped mixing “oil and vinegar” and throwing emotional Brexit politics on to what he said was essentially a technical problem. Lamy said he did not understand the UK’s strategy, which risked a trade war with the EU, but added that it was unlikely to come to this as the “cost-benefit ratio” was “ridiculous”. If matters did deteriorate and the EU retaliated with sanctions, the bloc would win as those with greatest capacity for trade generally did, Lamy said. His comments, in an interview with the Guardian, came after the British foreign secretary, Liz Truss, threatened new laws to allow the UK to change some of the Northern Ireland protocol. The UK government has come under pressure from the Democratic Unionist party and the Traditional Unionist Voice, both of whom campaigned on an anti-protocol ticket in the recent Northern Ireland assembly elections. Lamy, who has followed Brexit closely over the past seven years, and who is now president of the Paris Peace Forum, a French non-profit organisation, after leaving the WTO in 2013, said demands to remove the border in the Irish Sea completely would never deliver a breakthrough. “I don’t understand exactly what they [the UK] are after,” he said. “If it is no border it won’t work. You cannot leave the EU and not have a border. That’s just having your cake and eating it. “So there is a question mark as to what exactly is the problem on the UK side. If it is ‘we don’t want a border’ then it is like saying: ‘We don’t want Brexit.’ Then this is unsolvable.” Lamy continued: “The UK government has this capacity to mix problems and to cook a political soup. “These are oil and vinegar issues between emotion and technicalities. Emotion is extremely high because Boris Johnson keeps beating the drum to say Brexit is a great thing. He has to increase the sound of the drum to say Brexit is a great thing all the time.” If the UK admitted a border was the direct consequence of Brexit, then a solution could be found, Lamy said. There could be a dynamic solution for Northern Ireland, he suggested. This would involve a “thin border” with few checks on trade across the Irish Sea while the UK remained aligned to EU standards. This would become a “thick border” if the UK wanted to diverge from those standards, Lamy added. This solution would require equivalence in standards with the EU and has already been rejected by the UK as unacceptable because it would compromise the country’s control of its own laws. Lamy said this went to the core issue of borders between nations and always involve tradeoffs. “The UK are torn between their political position, which is they want to have the capacity to diverge [on standards], and the technical consequence of that, which is a thicker border,” he said. The only way to solve the issue was to “dial down the emotion” and “let the technicians find the solution that allows both sides to find a midway between a thick and a thin border”. Given the border between the UK and the EU was not negotiable, the UK’s best shot at a solution was to “play for time, as you can’t play with money”, Lamy said. Solutions included trusted trader schemes that would would “transport the border up the value chain” and light-touch checks at ports. “Customs officers only have a limited amount of time in the day. It’s about finding a compromise between ensuring control on one side and trade to flow on the other,” Lamy said. He played down the UK’s threat to legislate to “disapply” some of the protocol if the EU did not concede to Johnson’s demands, saying he found it difficult to believe the UK and the EU would end up in a trade war. “If there was one, the EU would win as generally the one that has the largest trade capacity prevails,” Lamy said. With war in the Ukraine and Sweden and Finland making the momentous decisions to join Nato, Brexit was an “irritant” to EU leaders, he added.