The British government has ruled out moving the Border to the Irish Sea after Brexit by imposing customs checks between Northern Ireland and Britain. The department for exiting the European Union said that, although finding a solution for the Border was a top priority, moving controls to ports and airports in the North was out of the question.

“As we have always been clear, our guiding principle will be to ensure that – as we leave the EU – no new barriers to living and doing business within the UK are created. Therefore we cannot create a Border between Northern Ireland and Great Britain,” a spokesperson said.

“We aim to have as frictionless and seamless a Border as possible between Northern Ireland and the Republic of Ireland and we welcome the European Council’s recognition that flexible and creative solutions will be required. It is our priority to deliver a practical solution that recognises the unique social, political and economic circumstances of the Border.”

The future of the Border has emerged as the point of strongest disagreement between the British and Irish governments over Brexit, with Minister for Foreign Affairs Simon Coveney expressing scepticism about the capacity of technology to ensure that customs controls would be frictionless. Mr Coveney met Brexit secretary David Davis in London earlier this month and the two men had an exchange which was described as “blunt and frank”.

A few days later, Mr Davis told the House of Lords EU committee that the change of personnel at the top of the Irish Government had “slightly stymied” technical work that had started on making customs controls on the Border as unobtrusive as possible.

“I saw Mr Coveney, the new foreign secretary, the other day, and we started that discussion again, as it were, from scratch,” he said.

Favoured option

EU diplomatic sources told The Irish Times on Friday that the Government did not explicitly propose moving the Border to the Irish Sea at a recent EU summit. British officials are aware, however, that the Government’s favoured option is to extend the EU customs union to include Northern Ireland, effectively moving the Border to the Irish Sea.

The proposal is unacceptable to the DUP, on whose 10 votes at Westminster the Conservative government depends for its survival. The DUP’s leader in the Commons, Nigel Dodds, on Friday described the idea as untimely and unhelpful and made clear that his party would block it.

“The DUP will not tolerate a Border on the Irish Sea after Brexit that makes it more difficult to live, work and travel between different parts of the United Kingdom. The prime minister has already reiterated this. At Westminster we will continue to use the influence of our 10 MPs to ensure that respect for the integrity of the UK remains at the core of the negotiations process,” he said.

The chancellor of the exchequer Philip Hammond said on Friday that Britain would seek a transition arrangement lasting up to three years after Brexit, during which its relationship with the EU would appear almost unchanged. Mr Hammond said a consensus was emerging in the cabinet in support of an arrangement under which Britain would continue to have full access to the single market but would also continue to allow free movement of people from the EU.