Boris Johnson will act unilaterally to give supermarkets and their suppliers more time to adapt to post-Brexit trade arrangements in Northern Ireland in a major escalation of tensions with Brussels.
The Prime Minister told the Commons: "The position of Northern Ireland within the UK internal market is rock solid and guaranteed... We leave nothing off the table in order to ensure we get this right."
Brandon Lewis, the Northern Ireland Secretary, confirmed that the UK is extending the grace period for supermarkets agreed with the EU last year by six months.
The move sparked a fresh row with the EU, which is jointly responsible for the Northern Ireland Protocol governing trade and new border checks in the province.
The European Commission said the EU had "strong concerns" over the unilateral move because "this amounts to a violation of the relevant substantive provisions of the Protocol on Ireland/Northern Ireland and the good faith obligation under the Withdrawal Agreement."
"This is the second time that the UK government is set to breach international law," said Lord Frost's opposite number Maros Sefcovic, referring to earlier UK threats to override the Withdrawal Agreement.
The commission threatened retaliation through enforcement measures in the Withdrawal Agreement and trade deal in response.
The temporary relaxation for checks on supermarkets and their suppliers had been due to expire at the end of this month under the terms of Northern Ireland Protocol, which is part of the Withdrawal Agreement reached in 2019 and which came into force this year.
However, in a written ministerial statement published on Wednesday, Mr Lewis said suppliers moving goods between Great Britain and Northern Ireland will now not be required to fill out the extra paperwork for agrifoods when the deadline expires.
Instead, the UK will unilaterally extend the deadline until October while continuing to try to secure agreement with the European Commission for a longer extension as requested by Michael Gove.
The Telegraph also understands that the UK intends to pursue other unilateral measures later this week, including extending the grace period for parcel couriers and solving issues with importing plants, vegetables and agricultural machinery with British soil on them.
The UK is currently in discussions with the European Commission over its demands to extend a number of grace periods for supermarkets, chilled meats, medicines and parcels until January 2023. It hopes to use the additional time to try and find permanent solutions to the problems being experienced by traders at the border.
These issues are supposed to be agreed jointly through the joint committee, which is chaired by Lord Frost, the minister in charge of EU future relations, and his Brussels counterpart, Maros Sefcovic.
Lord Frost spoke with Mr Sefcovic on Wednesday night and informed him that the measures taken were "temporary technical steps" and were "precedented in other trade arrangements".
A government spokesman said: "He underlined that these were needed for operational reasons and were the minimum necessary steps to allow time for discussions to continue without [causing] disruption in Northern Ireland."
With Brussels warning that any concessions are conditional on the UK stepping up checks at the border, Mr Johnson and his senior ministers have signalled that they will begin ratcheting up pressure on the EU to change course.
The latest move was interpreted as a major escalation. Irish Minister for Foreign Affairs, Simon Coveney said, “A unilateral announcement is deeply unhelpful to building the relationship of trust and partnership that is central to the implementation of the Protocol."
An EU diplomat said: "British diplomacy is very predictable these days: Choose confrontation. Because why on Earth would you want to respect an agreement you negotiated yourself? And why on Earth would you want to settle difficult issues in an amicable way if you can also take a confrontational approach?"
Another diplomat said: "Frost is acting as we expected. Under the agreement, a grace period can only be agreed by both sides. If it's not, it’s not a grace period but a violation of the treaty."
Whitehall sources denied it was a breach of the protocol, adding that the measures were necessary to avoid a "cliff edge" for businesses.
The UK will continue to engage through the joint committee but, with little progress made, said it was necessary because supermarkets begin to make stocking decisions one month in advance. It will not require triggering Article 16 of the protocol, a measure of last resort enabling one side to override parts of the agreement.
"At the moment, unfortunately, we are not seeing from the EU the pragmatism required to make the protocol work for the citizens of Northern Ireland," a Government source said.
Aodhán Connolly, the director of the Northern Ireland Retail Consortium, said businesses welcomed the extensions even if they were unilateral. He said they would allow retailers to continue giving Northern Ireland households choice and affordability but called on both sides to agree a permanent solution.