The Secretary of State failed to take the Paris Agreement into account when making his decision on the third runway at Heathrow

The Court of Appeal (Lindblom, Singh, Haddon-Cave, LLJ) has determined that the Secretary of State erred in law in failing to take into account the Paris Agreement on climate change before designating the Airports National Policy Statement ("ANPS") and that his failure to do so was legally fatal to the ANPS.

Pursuant to section 5(8) of the Planning Act 2008 ("the Act"), the Secretary of State was under a statutory duty to explain how the ANPS took account of  "Government policy relating to the mitigation of, and adaptation to, climate change." The Court considered that the words "Government policy" should be applied in their ordinary sense to the facts of a given situation – thus, there was no basis in the statute for limiting the phrase to the legal requirements of the Climate Change Act 2008. The concept of policy is necessarily broader than legislation. The Court determined that the Government's commitment to the Paris Agreement was clearly part of "Government policy" at the time of designation of the ANPS, given (a) the UK had ratified that agreement in November 2016 and (b) the firm statements made by relevant Ministers reiterating the Government policy, including Rt. Hon. Andrea Leadsom MP and the Rt. Hon. Amber Rudd MP in March 2016.

The Court of Appeal accepted that the Secretary of State made an error of law because he never considered that he could take into account the Paris Agreement pursuant to his statutory obligations in section 10 of the Act. That section requires the Secretary of State to exercise his functions under section 5 of the Act "with the objective of contributing to the achievement of sustainable development" (s 10(2)); and in so doing, he must have regard, in particular, to the "desirability of mitigating, and adapting to, climate change" (s 10(3)). The Court further determined that the Paris Agreement was so obviously material that it had to be taken into account.

Finally, the Court decided that the Secretary of State also breached the Strategic Environmental Assessment ("SEA") Directive and Regulations by failing to consider the Paris Agreement - pursuant to Article 5(1) and Annex 1(e) "environmental protection objectives" established at the international level would include those in unincorporated international agreements such as Paris.

Regarding relief, the Court considered that a declaration was appropriate, the effect of which will be to declare the designation decision unlawful and to prevent the ANPS from having any legal effect unless and until the Secretary of State has undertaken a review of it in accordance with the statutory provisions, including the provisions of sections 6, 7 and 9 of the Act.

39 Essex Chambers' Nigel Pleming QC, Catherine Dobson and Stephanie David are representing five local authorities, Greenpeace and the Mayor of London.