British Prime Minister Boris Johnson will on Wednesday reveal his new Brexit plan to EU leaders, which will include "two borders for four years", meaning that Northern Ireland will remain in a special relationship with Europe until 2025.
The plan, which was leaked to The Telegraph, will accept the need for a regulatory border between the UK and Northern Ireland in the Irish Sea for four years, and Customs checks between the north and the Republic of Ireland.
The EU and Ireland are opposed to the Customs checks proposal.
Mr Johnson’s additions are replacements for the existing Irish backstop, the controversial insurance policy that ensures the border on the island stays open even if there is a no-deal Brexit.
His plan means that Northern Ireland will remain in the EU single market until at least 2025 but will leave the EU Customs union alongside the rest of the UK.
After the four years, the Northern Irish Assembly will be free to choose whether to remain aligned to the EU or return to following British rules, which by that time are expected to be different to those in Brussels.
On Tuesday evening after the proposals were published, Ireland's Foreign Minister Simon Coveney said they would not provide the basis for a deal with the EU and were "concerning".
"We haven't seen anything but if the reports we are reading this evening are true, it doesn't seem like the basis for agreement, that's for sure," Mr Coveney told Ireland's Virgin Media One TV.
Other EU members are also likely to oppose the deal. They believe such an agreement would risk breaking the Good Friday Agreement and the integrity of the single market.
Mr Johnson will tell EU leaders that it is his final Brexit offer, and if Brussels does not engage with him he will try to take Britain out of the bloc without a deal.
Addressing his Conservative Party’s annual conference in Manchester, England, the prime minister said he would issue an ultimatum to Brussels.
Mr Johnson is vowing to defy efforts by the British Parliament to prevent a no-deal exit.
His office said on Tuesday that he would never negotiate the extension to EU membership that new legislation demanded if he could not secure an agreement.
If he cannot get a deal and does not seek a delay, he will probably find himself fighting members of Parliament in court and could even be removed.
“The prime minister will in no circumstances negotiate a delay,” his office said.
Mr Johnson will describe his offer as a “fair and reasonable compromise” to which both sides can agree.
His office said this would be his final proposal and, if rejected, the UK would begin preparations for a no-deal Brexit.
This week Tory MPs who refused to vote for the agreement that Theresa May negotiated suggested they could be persuaded to back a deal to avoid losing Brexit altogether.
The Democratic Unionist Party, a key ally from Northern Ireland, has been publicly supportive of Mr Johnson and his efforts.
The prime minister said at the conference alongside DUP figures that he hoped to clinch a deal in the next few days.
Mr Johnson set a new 10-day deadline for reaching a deal, he told the The Sun newspaper, published on Tuesday.
Meanwhile, it emerged that European governments have privately discussed allowing a time limit on the Irish backstop, sources said.
But that limit would only be on offer if Mr Johnson put forward a workable proposal, officials said.
