When mitigation matters … timing and the Habitats Directive

An important question of when mitigation measures should be taken into account in the planning process has been clarified in the High Court on 14th May 2019 in the comprehensively titled Canterbury City Council v Secretary of State for Housing, Communities and Local Government v Hollamby Estates (2005) Limited, Crondall Parish Council v Secretary of State for Housing, Communities and Local Government, Crondall Developments Limited v Hart District Council [2019] EWHC 1211 (Admin).

For those unfamiliar with the terminology, Appropriate Assessments form part of the regime established under European Directive 92/43/EEC ("the Habitats Directive"). This identifies a range of protected habitats across Europe (the Natura 2000 network) and sets out steps which must be followed if any plan or project is likely to have a significant effect on one of these European Sites. The Directive is transposes into UK domestic law by the Conservation and Habitats and Species Regulations 2017.

Under Article 6(3) of the Habitats Directive, the effects of a plan or project on a European Site are considered in two stages. The first is the 'screening' stage. If this finds that the plan or project is likely to have a significant effect, the second stage (an Appropriate Assessment) is required. The decision taker can only agree to the plan or project proceeding if it will not adversely affect the integrity of the site concerned (except in some exceptional circumstances).

The Appropriate Assessment regime has been given significant judicial consideration at the European and national level. On screening stage and mitigation measures, the position of the European Court of Justice is clear. Using an inescapable logic familiar to those acquainted with the pages of Catch 22: to take account of mitigation effects at the screening stage presupposes a likely significant effect on the European site in question. If a likely significant effect is presumed, the terms of Article 6(3) are already made out and QED Appropriate Assessment is required.

Less flippantly, as the judgement explains, taking account of mitigation methods at the screening stage pre-empts the outcome of the Appropriate Assessment. This effectively extinguishes any detailed assessment of effects on the site, circumventing the procedural safeguards provided by the Habitats Directive and deprives the Directive of its purpose. For these reasons such an approach has been resisted by the courts.

In the current cases, mitigation measures had been undertaken at the screening stage. As such both were in clear breach of European environmental law (and hence, in UK judicial review terms 'illegal'). However, while one of the appeals went on to be upheld, the other was quashed. This is because the court also retains the discretion not to quash decisions on the ground of illegality, if the decision-taker can demonstrate that the decision reached would inevitably have been the same in the absence of the error. In the Canterbury case, this was found to be so, and the decision was not quashed. The same test was not, however, passed in the Crondall case, where the Defendant's decision was subsequently quashed.

The judgment serves as an important reminder of several factors:

• The decision as to whether an Appropriate Assessment is required or not, cannot be swayed by the impact of any potential mitigation measures, but must be based on the development alone. Any mitigation measures can, of course, be considered at a later stage of the assessment, and an otherwise unacceptable project could still potentially be granted permission if mitigation is sufficient;
• Secondly, even if illegality is found, this will not inevitably lead to a decision being quashed. This will depend on whether the decision would inevitably have been the same, even with the error rectified;
• Finally, the case also serves as a reminder that at present European environmental legislation continues to play an important part in development decisions. However, if the UK does leave the bloc, this may change significantly.

This article is for general guidance only. It provides useful information in a concise form. Action should not be taken without obtaining specific legal advice.