It is a pleasure to follow the right hon. Member for West Dorset (Sir Oliver Letwin), and I welcome the fact that he thinks this is a debate about means not ends. The debate should continue in that constructive spirit. I am particularly interested in his ideas for an environment Bill, presumably to be introduced before exit day, and his ideas about governance, which we will be debating in Committee on a later day. I rise to speak to new clause 67 because I have not been entirely convinced by the right hon. Gentleman. The aim of the clause is simple: to ensure that the environmental principles set out in article 191(2) of the treaty on the functioning of the European Union-the precautionary principle, the principle that preventive action should be taken to avert environmental damage, the principle that environmental damage should as a priority be rectified at source, and the polluter pays principle-continue to be recognised and applied after exit day, which is important. In that respect, new clause 67 is broadly similar in its intent to new clauses 60 and 28. If either of those new clauses is pressed to a vote, we would be minded to support them. The environmental principles set out in article 191 of the TFEU form an essential component of environmental law; they are not unique to environmental law, but they are principles of environmental law in general. The principles are also found in a number of international environmental treaties to which the UK is a signatory, including the convention on biological diversity, the convention on climate change and the convention on the law of the sea. At present, the UK gives effect to those obligations through its membership of the EU, and particularly through the Lisbon treaty. As the hon. Member for Brighton, Pavilion (Caroline Lucas) and the right hon. Member for West Dorset said, the principles play three key roles: they are an aid to the interpretation of the law; they guide future decision making; and they are a basis for legal challenge in court. The hon. Member for Brighton, Pavilion set out in great detail the wide range of areas in which the principles have led to tangible environment improvement benefits. As it stands, the Bill does not ensure that the environmental principles will be recognised and available in domestic law after exit, and as such does not retain those three key roles. The principles are not preserved by clause 4 because they do not confer directly effective rights on individuals. According to the legal advice that I have received, neither do they fall within the definition of the general principles of EU law that are to some extent preserved by the Bill, although the Minister may want to comment on that. Whereas the general principles apply across all EU law, by their very definition some environmental principles apply only to environmental law and policy. If we are to retain the law we have, to be effective custodians of the environment and to be world leaders when it comes to environmental standards, it is imperative that we embed the principles in the way policy operates. To his credit, the Secretary of State for Environment, Food and Rural Affairs has recognised that. However, the Government have argued that environmental principles are interpretive principles, and that as such they should not form part of the law itself. I argue that the environmental principles are not simply guidance; as the hon. Member for Brighton, Pavilion mentioned, they have been given effect in EU law. Article 11 of the TFEU states:“Environmental protection requirements must be integrated into the definition and implementation of the Union policies and activities, in particular with a view to promoting sustainable development.â€They are, therefore, a vital aid to understanding the role and function of existing legislation, as well as being an interpretative tool for decision makers and, if necessary, the courts. For the principles to have equivalence on exit day, they must be placed in domestic legislation. I recognise that a consultation on this subject has been announced, but it will not report back before the Bill has progressed through this place. There is good reason to doubt that the direction of travel being signalled by the Government-namely, a reliance on UK case law, judicial review and some form of policy guidance-will do the job, even if all that operates alongside governance arrangements in the form of an as yet undefined watchdog, although the right hon. Member for West Dorset gave some valuable insight into what the Government are thinking in that respect. UK case law is unlikely to retain and capture the effect of all the principles set out in article 191, as that would limit enforceability to where the principles already exist in case law. It is difficult to see how judicial review, which looks only at the legality of a decision or action rather than its scientific merits, will materially apply core environmental principles. Likewise, reliance on policy guidance-something explicitly referred to by the Secretary of State recently in evidence to the Environmental Audit Committee-is arguably an inadequate basis on which to proceed. As the hon. Member for Brighton, Pavilion noted, policy guidance is necessarily limited in scope, but there is a strong case for ensuring that environmental principles apply across Government, informing law as well as policy, to match the rigour of the treaty obligations. Policy guidance also entails a weaker duty on public bodies: policy statements are only guidelines or material considerations for public bodies to consider, meaning that they are less likely to influence a decision than a strict duty to comply. Policy guidance is impermanent; it is prey to changes resulting from short-term political agendas-under different Ministers and different Governments-and so does not provide long-term certainty, and it lacks the binding character of statute. There should be a clear duty to comply with environmental principles in statute, to match the current strong legal obligation set out in the treaty, and the courts should be able to enforce such a duty.