DUP leader Arlene Foster has written to the leaders of all 27 EU countries, telling them that Northern Ireland will not tolerate any difference in status between itself and the rest of the United Kingdom after the UK leaves the EU.

Earlier this week, it had been suggested that Northern Ireland might remain in the customs union after Brexit, to prevent a hard border between itself and the Irish Republic. But, speaking to the DUP annual conference in Belfast, Ms Foster made clear that Northern Ireland would leave the customs union.

She said: “We will not support any arrangements that create barriers to trade between Northern Ireland and the rest of the United Kingdom or any suggestion that Northern Ireland, unlike the rest of the UK, will have to mirror European regulations.

Northern Ireland already has special customs union rules, Michel Barnier says

“I have written to the heads of government of each of the EU 27 member states setting out our views.”

Irish Prime Minister Leo Varadkar has said he will not allow Brexit negotiations to move on to trade until the Irish border issue is settled, and no one has yet offered a workable solution to the question of no hard border in Ireland, while one side of it remains in the EU’s customs union and the other does not.

It has been suggested that Ireland’s geographical border could serve as a de facto border, but Ms Foster rejected any such plan.

“The economic reality for our economy is that our most important trading relationship is with the rest of the United Kingdom and we will do nothing that puts that at risk in any way.

“We welcome the assurances from the Prime Minister and the UK Brexit team that no such internal barriers will be countenanced and that as we joined the then European Community as one nation we will leave as one United Kingdom.”

The DUP and Sinn Fein have still failed to form a government, 10 months after elections to the Northern Ireland’s Assembly at Stormont, which returned more nationalists than unionists for the first time ever.

Ms Foster did not hold back in her criticism of Sinn Fein, accusing them of “glorying in the murder of the IRA”.

She added: “My thoughts are with the victims of Enniskillen, Kingsmills and La Mon and the many thousands of innocent victims who have conducted themselves with such dignity over the decades.”

One of the key stumbling blocks in the return to talks are over Sinn Fein demands for recognition of Irish language and culture. Ms Foster said she had been willing to set up a power sharing agreement with “no conditions” and deal with language and culture issues “in parallel” but she told her Sinn Fein counterparts: “I respect the Irish language and those who speak it. However, respect isn’t a one-way street. Respect works both ways.