Laws about environmental protections after Brexit should be revealed by the government, 36 leading organisations including Greenpeace and RSPB have warned.

Not disclosing the information “is wholly at odds with the public’s right to information”, the organisations said in a joint letter to the Environment Secretary, Theresa Villiers.

The draft Environment (Principles and Governance) Bill establishes the Office of Environmental Protection (OEP) which will investigate complaints about public authorities breaking environmental laws after Britain leaves the European Union (EU).

The previous environment secretary, Michael Gove, said in December that the UK’s environment laws would be enhanced after Britain leaves the bloc.

However, a cross-party committee of MPs said proposed protections fell “woefully short”. A highly critical report found the OEP lacked independence from Defra and had limited powers.

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Although the OEP would have to reveal that it was investigating a particular authority most other information would be withheld.

In their letter, the organisations said this “would impose a degree of secrecy which does not apply to any other UK environmental regulator”.

Rebecca Newsom, head of politics at Greenpeace, told The Independent: “Releasing information for public scrutiny is a key pillar of our democracy. If ministers can dictate what the new environmental watchdog can or cannot disclose, that’ll be the first step towards muzzling it. This new agency will bear the huge responsibility of replacing powerful institutions like the European Commission in enforcing rules and targets on pollution and nature protection after Brexit, so it’s absolutely vital for the public to be able to see it operate effectively.

“Britain prides itself on having some of the strongest transparency laws in the world, and the new nature watchdog should be no exception.”

The public has a right to access environment information under the UK’s Environmental Information Regulations (EIR), the letter states.

Information is withheld if disclosure adversely affects the investigation but the information must still be released if the public interest favours disclosure. However, none of these conditions apply to the draft bill.

The letter, which has been co-ordinated by the Campaign for Freedom of Information, says: “If the OEP, public authority or minister (as the case may be) did not wish the information to be released, it would be withheld. There would be no need to show that disclosure would be harmful. The public interest in the information would be irrelevant. This would reverse decades of progress in opening up environmental information.”

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Amnesty International, Buglife, Bumblebee Conservation Trust, Campaign for National Parks, CPRE, ClientEarth, Compassion in World Farming, Friends of the Earth, Global Witness, Greenpeace, RSPB, Sustain and Wild Justice, among others, have signed the letter.

James West, Senior Policy Manager at Compassion in World Farming UK told The Independent: “As we leave the EU, Britain must ensure that there is no diminution of standards around animal welfare or environmental protections. It is vital that citizens can be confident the decisions reached by the OEP when investigating public bodies, particularly on something as critical as environmental protection, and therefore transparency is required.