This depends, to some extent, on the terms reached with the EU as part of Brexit negotiations.
If the UK seeks to remain a member of the European Economic Area (‘EEA’) and the European Free Trade Association (‘EFTA’) in an approach similar to that taken by Norway, it is likely that it will be required to comply with most European legislation. For instance, EEA members are required to comply with the EIA and SEA Directives but are not required to comply with the Habitats Directive. In the event that the UK seeks to remain only a member of EFTA in an approach similar to that taken by Switzerland, there will likely be more scope for flexibility.
Alternatively, if the UK chooses to operate outside of these regimes and/or forges a bespoke relationship with the EU following Brexit, it is possible that the EU Directives will cease to influence UK law. Notwithstanding the transposition of the EU Directives into UK law through the Regulations (which were enacted under the European Communities Act 1972, which may be repealed) it is anticipated that Parliament would need to take positive action to maintain the status of the Regulations following Brexit. Therefore, there is a possibility that the Regulations could lapse following Brexit. There are, however, other factors in play which make it likely that the Government will seek to maintain a requirement for environmental assessment as part of the UK planning system. In particular, the UK’s international treaty obligations will continue after Brexit and include the Convention on Access to Information, Public Participation in Decision Making and Access to Justice in Environmental Affairs (the ‘Aarhus Convention’) which requires public participation in environmental decision-making and access to environmental information. These obligations are, at least in part, met through the provisions of the EIA Regulations and the SEA Regulations.
Nevertheless, in this scenario, the Government would undoubtedly have more scope to change the approach to the assessment process to suit circumstances in the UK. This may result in some changes to the environmental assessment regime (perhaps so as to lighten the burden on developers and local planning authorities by, for instance, raising the thresholds at which an EIA is required), even if the regime is not removed entirely. Interested parties in the UK would also be more empowered to influence the form of any new regime, given that the Government would be responsible for effecting any such changes directly rather than simply channelling EU Directives.