A coalition of leading environmental groups says there is a “significant risk” that British environmental protections will be reduced after Brexit, despite the government’s positive rhetoric.

Greener UK, which represents 13 campaign groups including WWF, National Trust, RSPB, Friends of the Earth, Green Alliance and the Wildlife Trusts, says there are “serious concerns” that the government will not cooperate with the European Union after Brexit on environmental issues which need international agreement. Although the environment secretary, Michael Gove, has made several recent announcements, such as the 5p levy on plastic bottles, Greener UK believes there may be a “lack of willpower to ensure high standards across the UK”.

Shaun Spiers, the chairman of Greener UK and executive director of Green Alliance, praised Gove as a “highly engaged and effective environment secretary” and welcomed the prime minister’s promise to put the environment at the centre of government policy.

“Yet these green aspirations have not carried over to the government’s narrative on Brexit,” Spiers said. “There are serious concerns about the level of future co-operation between the UK government and the EU, and the impact this will have on issues such as climate change and air quality. We also fear there is a lack of willpower to ensure high standards across the UK when we lose the common frameworks currently provided by the EU.”

The warning comes as a rebel Conservative MEP told the Observer the UK was no longer working effectively with the EU on environmental issues. Julie Girling had the Tory whip withdrawn when she supported a European Parliament resolution saying the UK had not made sufficient progress in talks with the EU.

She said: “Since before the June 2016 referendum, from March when we had purdah, they have stopped engaging with MEPs. People in the European council and commission have told me that’s the case for them as well.

Julie Girling: ‘In most cases Defra officials are not saying anything at all.’ Photograph: Geoff Pugh/REX

“Until I had the whip withdrawn, we [Conservative MEPs] were told that it’s business as usual, we’re still a member, but that’s not been the case for the government.”

She said that until the referendum campaign began, officials at Defra were engaging on a daily basis with their counterparts in the EU about all sorts of issues. “If discussions are happening now, they are happening offline because in most cases Defra officials are not saying anything at all,” Girling said. “They are not prepared to discuss details on anything.”

Two EU directives are receiving significant scrutiny without any real UK input, Girling said: the renewable energy directive, which relates to biofuels and member states’ targets for renewable energy; and the energy efficiency directive on building standards.

She said that MEPs and environmental lobbyists from other EU countries had told her that they had heard very little from the UK on these issues – a significant change from previous EU policy debates.

Part of the problem, campaigners say, is the lack of resources available to Defra, which has been given an extra £94.4m for managing Brexit, yet is also facing budget reductions of £147m by 2019.

Spiers said that the government’s pledge to be a global leader on plastic waste was undermined by the “swingeing cuts” to Wrap, the waste and resources action programme that is responsible for reducing waste. Wrap is losing a tenth of its staff to budget cuts.

“There are big questions about whether the government is willing to devote the resources necessary to deliver a green Brexit,” Spiers said.

Professor Charlotte Burns, a professorial fellow at Sheffield University who works on environmental policy, said: “What you’re asking Defra to do is take over responsibility for a whole lot of areas that were previously the EU’s responsiblity but without the staff base necessary to do it. That’s a real challenge we are facing as a country.”

Campaigners believe many improvements to the environment have happened only because successive governments have been spurred into action by the prospect of being taken to the European court of justice.

In November, Michael Gove announced that the government would create a “world-leading” environmental watchdog, backed by statute, to deliver Brexit.

“Michael Gove’s commitment to creating an environmental watchdog is good,” Burns said, “but we’ve seen other committees being ignored or shut down if they make too much fuss.”

The Sustainable Development Commission was shut down by the coalition government in 2011, while the “independent and well-respected” Committee on Climate Change had seen its last two reports effectively ignored by the government, Burns said.