Transport Secretary Grant Shapps has asked for another six months before making a decision on plans to dual a 13-mile stretch of the route.
The update was relayed to the House of Commons in a statement by transport minister Andrew Stephenson on Monday.
The decision on the Development Consent Order required for the scheme to progress is now expected on December 5.
The delay follows the publication of Sir Peter Hendy’s Union Connectivity Review.
Mr Shapps said: “We are considering his recommendations carefully, and have been working with the Scottish Government, Welsh Government, Northern Ireland Executive and key stakeholders, to identify the solutions that work best for the people of the UK. We expect to publish the UK Government’s response later this year.
“Several of the Union Connectivity Review recommendations concern ongoing projects, which may be impacted by the Union Connectivity Review response.
"The A1 Morpeth to Ellingham scheme is one such case, as it relates to Sir Peter’s recommendation for a multimodal study of the East Coast Corridor to identify the best opportunities for improvement.
"We therefore propose to consider how best to align the future progression of the scheme with our consideration of this recommendation and the outcome of any study that may be proposed.”
Berwick MP Anne-Marie Trevelyan has expressed disappointment at the further delay.
She said: "Whilst it is clearly disappointing that we must wait a little longer for the official go ahead for the A1 dualling project, I am really pleased Ministers are taking the Union Connectivity Review into account.
"Dualling the A1 to the Scottish border - my long-term objective - was one of the core messages of my submission to the Union Connectivity Review, and having spoken to Grant Shapps about this yesterday (Monday), I know he is determined to ensure long-term investment in our road networks and linking the A1 project to the UCR is key to that."
But Cllr Gordon Castle, Alnwick ward member on Northumberland County Council, said: “I am unable to accept or defend this ministerial statement, yet another attempt to bury an urgently needed decision under the sand.
"It is essential for the minister to make it crystal clear that the A1 dualling north of Morpeth, already funded, will go ahead regardless of the outcome of any additional work on improved Union Connectivity, which may be welcome but is not funded.
"Not to do so fuels the fires warming those cynics whom I’m tending to join. What happened to levelling up? This project was a major Conservative Party project that must be delivered as promised if any credibility is to remain with government manifesto promises up here.”
The proposed development comprises the dualling of a nine-mile stretch between Morpeth and Felton and a four-mile section between Alnwick and Ellingham.
National Highways stated: “The Secretary of State has asked for more time to consider our proposals for upgrading the A1 between Morpeth and Ellingham in Northumberland.
“We remain committed to delivering these improvements and remain confident that our proposals will provide much needed additional capacity, with better connectivity for people and business, and safer journeys for everyone.
“We will carry on working with local authorities, landowners and other stakeholders along the route to ensure the continued development of this project while we await the Secretary of State’s decision, and thank them for their valuable input so far.”
The Transport Secretary had already delayed a final decision from January to June to allow for further consideration of environmental matters.