Hedgehogs, yellowhammers and dormice did not figure highly in the EU referendum campaign, but they may turn out to be some of the first losers from Brexit. Rules on farmers cutting hedgerows and field margins that have protected the habitats of a variety of at-risk species are being lost amid the biggest shake-up of nature regulations in four decades.

For three years, ministers have been proclaiming that leaving the EU would allow Britain to strengthen its environmental protections, and that all the benefits of membership would be faithfully carried over. Now we can see the worth of those promises, in a trio of bills set before parliament. The environment bill, agriculture bill and fisheries bill replace the EU’s comprehensive framework directives, common agricultural policy and common fisheries policy.

All three bills contain major flaws that undermine the government’s claims. They leave gaps, fail on enforcement and oversight, open loopholes for future ministers to quietly backslide from existing standards, and turn what is currently a coherent system of long-term, stable regulation into a patchwork of competing and sometimes contradictory proposals.

Take the environment bill. It sets out four priority areas, some of them critical for human health: air quality, waste and resource efficiency, water and nature. Air pollution contributes to 40,000 deaths a year, and the new bill sets out a framework for standards on key pollutants. Yet although this bill could be law within a few months, the new standards on air – along with those on the other three priority areas – will not be set until October 2022.

The government says the delay is to give time for expert input. Parents struggling to get their breathless children to A&E every time there is a pollution spike might take the view that the World Health Organization, the EU and academic studies around the world have already answered the questions over what constitutes breathable air. Why do they have to wait more than two years without legal safeguards before even being allowed to know what the new limits will be?

‘Under the EU’s air quality directive, ministers were obliged not just to adhere to targets for air pollutants but to publish plans showing how the targets would be met.’ Photograph: Christopher Thomond/The Guardian

The watering down does not stop there. Under the EU’s air quality directive, ministers were obliged not just to adhere to targets for air pollutants but to publish plans showing how the targets would be met. That was where campaigners scored their most notable victories, when they took the government to court over Britain’s filthy air and judges ruled the plans were not valid. The new environment bill dispenses with the need for detailed plans that can be weighed up by experts and used to hold government to account. Instead, ministers will be required only to set out the steps they intend to take, without accountability as to whether those measures are sufficient.

New powers have also been quietly inserted for the government to derogate from high standards at will. Clause 81 of the environment bill gives the secretary of state powers to weaken targets for the chemical status of our water, either by relaxing the targets or changing the rules by which they are measured.

To reassure the public – who will no longer be able to take the government to the European courts over any failures – there is to be a watchdog, the Office for Environmental Protection. Will it have the same powers as the European courts? No. Will its judgments be binding? Not necessarily. Who will make up its board? Ministers will decide.

The agriculture bill and the fisheries bill, while containing some admirable aims, are also worrying. The EU’s common agricultural policy was often disastrous for wildlife and nature, and the government was rightly cheered when it proposed paying farmers for providing public goods – clean water, good soil, flood protection. But the new system of environmental land management contracts – to be phased in over seven years – will be voluntary and the measures farmers will be required to take will be decided at the level of individual farms. This leaves gaps.

Currently, there are specific protections for species and habitats that apply across the UK. Under environmental land management contracts, many of those protections – like the ones for nesting birds and hedgehogs – will become voluntary. Farmers could pick and choose what protections they sign up to, and those who do not want the public money could opt out altogether. And who will monitor the farmers who do? With ministers wanting to cut the number of farm inspections, enforcement looks hazy too.

Jettisoning the EU’s common fisheries policy also offered ministers a chance to stop rampant overfishing. They have not taken it. The bill retains a broad aim to restore stocks to “maximum sustainable yield” – the level, worked out by scientists, at which fishing does not harm the ability of the fish population to reproduce. But the fishing quotas each year are still to be set by ministers, with the power to depart from that scientific advice, and to choose which stocks will be fished sustainably and which will not.

Unless the government accepts amendments to these vital bills in the coming weeks and months, the UK will be quietly swapping an agreed set of outcomes and stringent environmental protections for a set of vague promises, voluntary measures, and deliberately loose and leaky legislation. Hedgehogs and voles will not be the only losers.

• Fiona Harvey is an award-winning environment journalist for the Guardian