Northern Ireland will leave the EU’s single market and customs union with the rest of UK, its Secretary of State has insisted, in a slapdown to Brussels.

James Brokenshire ruled out any U-turn by insisting there would be no separate trading arrangements for the province – despite growing concerns about the future Irish border.

This week, the European Parliament will side with Dublin by calling for customs checks to take place at Irish Sea ports for visitors travelling between Great Britain and Northern Ireland.

The resolution, set to be voted on hours before Theresa May’s make-or-break Tory conference speech on Wednesday, is expected to rubbish Britain’s existing border proposals.

But, at the Conservative conference in Manchester, Mr Brokenshire drew applause when he said: “We will leave the European Union in 2019 as one United Kingdom.

“That includes leaving the single market and the customs union, so that we can strike new trade deals with the rest of the world.”

Mr Brokenshire insisted he was committed to ensuring the “border for people, goods and services between Northern Ireland and Ireland remains as seamless and frictionless as possible with no physical infrastructure at the border.”

He claimed: “Significant progress has already been made as shown in Brussels last week.

“And with sufficient flexibility and imagination on all sides – as the EU itself has called for – we can succeed.”

It was also vital to ensure nothing “fractures the internal market of the United Kingdom, which benefits Northern Ireland hugely”, Mr Brokenshire insisted.

The upbeat prediction is not shared in Brussels, where EU leaders have accused London of “magical thinking” over the Irish border, with no workable proposal.

The Independent revealed last week that European Parliament chiefs believe shifting border posts to Irish Sea ports is the best way to break the deadlock over the issue.

They have dismissed Britain’s idea that spot checks could be carried out without any infrastructure at the border as incompatible with the rest of the UK leaving the EU’s trading bloc.