As the EU withdrawal bill inches its way through parliament, the environmental implications of Brexit are being revealed. Leaving the European Union could be the single most environmentally damaging act taken by government in the past half-century.

Almost all of the UK’s environmental policy derives from our membership of the EU. Across the full range of issues – air and water pollution, habitats and species protection, waste management and recycling, energy efficiency, carbon emissions and energy policy – it is EU regulation that has raised standards.

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Most current EU environmental law will remain in place – initially. But, unless specifically prevented by a future EU-UK trade agreement, a future government could weaken it. Recognising this danger, the secretary of state for the environment, Michael Gove, has promised a consultation on a new, independent body to enforce environmental law. But it is not clear if this will have the powers of the European commission and the European court of justice.

Environmental NGOs have started campaigning for new legislation. But the opportunity may be greater than they had recognised. Until recently, regulation has mainly worked by requiring businesses or products – farms, factories, buildings, cars – to cut waste and pollution. But the overall impact on the environment has not been controlled. Reductions have been outweighed by the counter-effect of economic growth and new products and processes.

The exception has been in the field of climate change. It is not just individual products and companies that are required to cut greenhouse gas emissions: whole countries are. Under EU law, and the UK’s own 2008 Climate Change Act, environmental limits have been imposed on our entire economy. The act requires the government to limit the total carbon emissions of the UK to levels set in law.

The Climate Change Act has been extremely successful. But climate change is not the only environmental threat

The revolutionary nature of this approach has not been widely understood. The Climate Change Act effectively places the UK economy under a sustainability constraint. Every five years, the government of the day is required to adopt a legally binding “carbon budget” setting limits on the total greenhouse gas emissions of the UK economy in a five-year period. Such budgets must be set for 15 years ahead, to give businesses and investors time to plan, and they must lie on a trajectory towards the long-term goal of an 80% reduction in UK emissions by 2050 (defined relative to 1990 levels).

The Climate Change Act has been extremely successful. But climate change is not the only environmental threat. Last month, the intergovernmental panel on biodiversity warned that human destruction of nature is rapidly eroding the world’s capacity to provide food, water and security to more than 3 billion people. The UK may be only 40 years away from the near-eradication of soil fertility. Our air pollution is estimated to shorten 40,000 lives a year.

A sustainable economy act should now be the new model. At its core would be a legal requirement on the government to set environmental limits, and to produce economy-wide plans to achieve them. Over time these limits should include air pollution, soil degradation, resource depletion, plastics pollution and biodiversity loss. All together they would bring the economy within a sustainability constraint.

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For each major environmental impact, the act would establish a long-term goal and require the government to set shorter-term targets and plans. So, for example, the 25-year goal of eliminating non-recyclable plastics would be implemented through a series of five-year plans to cut plastic waste by a specific number of tonnes. A long-term goal of restoring biodiversity to, say, a 1980 benchmark would be implemented through successive five-year targets for individual declining species.

The goals and targets would be based on the advice of an expert and independent sustainable economy commission, modelled on the climate change committee, which would in turn report to parliament.

It has now been 30 years since Margaret Thatcher warned that “no generation has a freehold on this Earth. All we have is a life tenancy – with a full repairing lease.” It is finally time to recognise the fundamental truth that environmental degradation arises from within our economy. Only by constraining it to live within the planet’s limits, in law, can we ensure a sustainable future.

• This article was amended on 6 April 2018 because a change made during the editing process led an earlier version to suggest that a sustainable economy act already exists.

