A High Court judge has issued an addendum judgment in the legal challenge to the A5 Western Transport Corridor road project, concluding that the Department for Infrastructure and the Department of Agriculture, Environment and Rural Affairs are now advancing a climate change case that is fundamentally inconsistent with the position they took when the original decision to proceed with the scheme was made.

Mr Justice McAlinden delivered the judgment on 11 March 2026, following a direction from the Court of Appeal to consider new affidavit evidence from DAERA and determine what responsibilities that department holds under section 52(1) of the Climate Change Act (Northern Ireland) 2022, and how those responsibilities relate to the functions exercised by DfI in authorising part of the A5 scheme.

The case has a complex procedural history. The judge's first judgment, delivered on 23 June 2025, quashed the DfI decision to proceed with a section of the road after finding an inadequate evidential base to support the department's assertion that estimated greenhouse gas emissions from the scheme's construction and operation would be specifically factored into Northern Ireland's plans to meet its statutory climate targets. DfI appealed, DAERA and Friends of the Earth were granted leave to intervene, and the Court of Appeal remitted specific climate-related questions back to McAlinden J. Further hearings took place in December 2025 and into early 2026.

At the original hearing, DfI had repeatedly stated that the estimated additional emissions from the road - projected at approximately 972,520 tonnes of CO2 equivalent across both construction and operational phases - had been carefully calculated and would be included within the Northern Ireland Executive's plans to remain within carbon budgets and meet reduction targets. The DfI Statement, finalised in October 2024 and agreed with DAERA input, explicitly committed that those emissions would be factored into plans to meet targets under sections 1, 3, 4 and 24 of the 2022 Act.

The new affidavit evidence, primarily from DAERA's Patrick Savage and NISRA statistician Hugh McNickle, now sets out that project-level emissions are not incorporated into the methodologies used to compile GHG inventories or project future emissions, and that doing so would result in double counting. Mr McNickle averred that the emissions projection tools used by Northern Ireland rely on macro-level economic and population variables, and that these tools robustly account for the scale of future construction activity without reference to individual projects. DAERA concluded in this evidence that it is not in a position to give any assurance around the specific implications of the A5WTC project on Northern Ireland's overall emissions pathway.

McAlinden J accepted that the court should not interfere with the methodologies and modelling used by departments provided they have a rational basis, and clarified that nothing in his first judgment required DAERA or other departments to incorporate project-level emissions into sectoral plans or the Climate Action Plan. Section 52 of the 2022 Act does not mandate such an approach, he said, nor does Part 3 of the Act or section 13.

However, the judge was emphatic that the case now being presented by DfI and DAERA is not the case that was made at the original hearing. He said it was impermissible for a government department to have a decision quashed on the basis that the evidential foundation for its stated position was lacking, and then to attempt to justify the same decision on appeal by reference to a fundamentally different case. He described the departments' suggestion that his original ruling reflected a misunderstanding of their position as "gaslighting", stating he had carefully and comprehensively analysed the case as it was actually presented.

The judge noted that during the second hearing he invited both departments to consider making a fresh decision on the basis of the new case, giving potential challengers the opportunity to scrutinise and, if appropriate, contest it with expert evidence. He adjourned the hearing to allow counsel to take instructions from ministers and departments. Both departments instructed counsel to proceed with the appeal. McAlinden J said this approach caused material prejudice to the original applicants and constituted an unprincipled approach to litigation. The judgment was prepared as an addendum to assist the Court of Appeal in its further deliberations.