According to the Institute for Government, the environment is the area where the UK is brought most often before the European Court of Justice (ECJ). In most cases, it is not a problem of transposition, but of implementation. Even though the UK will copy across the EU environmental acquis, the real issue is therefore the actual application, due to be monitored and enforced ensured by the Office for Environmental protection. Nevertheless, the office is already the target of critiques for lack of independence, specifically on its ability to take action against the government.
Furthermore, NGOs and British citizens could well be dissuaded to initiate litigations, as the judicial costs are lower within the ECJ than in UK national courts.
Institute for Government explainer on the level playing field in Brexit negotiations
Institute for Government briefing on the UK’s relationship with the European Court of Justice