BRUSSELS (Reuters) - Northern Ireland will not stay in the European Union’s single market or the customs union after Brexit, a British government official said, adding that arrangements for the border with Ireland must not eat into the United Kingdom’s integrity.

Britain's Northern Ireland Secretary of State James Brokenshire speaks to media outside Stormont House in Belfast, Northern Ireland November 1, 2017. REUTERS/Peter Morrisson

Allowing Northern Ireland to retain some access has been floated by the European Parliament’s Brexit pointman, Guy Verhofstadt.

“We will leave the European Union in 2019 as one United Kingdom,” the British minister for Northern Ireland, James Brokenshire, said on Monday. “We need to ensure that nothing is done that undermines the integrity of the UK single market.”

“I find it difficult to image how Northern Ireland could somehow remain in while the rest of the country leaves. I find it impossible,” he told a seminar in Brussels.

Brokenshire reiterated Prime Minister Theresa May’s insistence that the United Kingdom would be exiting both as a result of the 2016 referendum.

London has proposed an “invisible border” without checkpoints or immigration controls between EU member Ireland and Northern Ireland after Brexit. But it has given no firm ideas on customs arrangements and the EU has mostly been critical, seeing these plans as unrealistic.

Dublin has said it will not let Brexit negotiations move from the divorce talks to discussions about future trade relations between Britain and the EU - as London is pushing for - without more guarantees on the border.

Irish Foreign Minister Simon Coveney has demanded more guarantees that the Irish issue would be solved even if the future trade talks between Britain and the remaining 27 EU states collapse.

AGRICULTURAL LAWS

“Show us how it could be done in practise, how can you be outside of the single market and customs union and not have border infrastructure at the same time,” one EU diplomat said in Brussels. “It’s about where and how you will carry out checks.”

With London reluctant to accept controls between Northern Ireland and the rest of the United Kingdom, and both sides declaring determination to avoid a hard border between the two Irish communities, the person said the only remaining option would be to run checks between Ireland and the rest of the EU.

“That would complicate Ireland’s exports to the EU as everything would be checked as if it were coming from Northern Ireland, but maybe that would still be a less bad option for them than having a border on the island,” the diplomat added.

Brokenshire said some agricultural laws in Northern Ireland -- which is trying to reach agreement on how to relaunch its regional executive that is ruled at arm’s length from London -- were already different than elsewhere in the United Kingdom.

After meeting the EU’s top agriculture official in Brussels, Irish Commissioner Phil Hogan, Brokenshire signalled Belfast could keep some of its laws closer to those of the EU after Brexit to minimise trade disruptions across the future border.

He also said London was keen to preserve the common travel area Ireland has with Britain, as well as the single electricity market on the island of Ireland. He hoped for close cooperation with Dublin, including on security matters, after Britain leaves, as is now due to happen in March, 2019.

British and EU negotiators will meet in Brussels again this Thursday and Friday for more Brexit talks that have been grinding slowly, unnerving investors and businesses who seek clarity to plan their operations.

Brussels is growing sceptical that there will be enough progress in time for another gathering of all EU leaders in mid-December on the three main issues the bloc wants to settle before opening trade talks.

The question of the Irish border is one. The most politically contentious one is agreeing Britain’s divorce bill.

Most progress has been achieved in the third - setting mutual safeguards for Britons living in the EU after Brexit and EU citizens residing in the first country to ever decide to leave the bloc - but that is not yet settled either.