Andrea Leadsom’s appointment as environment secretary has raised significant concerns among senior environmental and agricultural figures over her suitability for the role.

Leadsom’s lack of top-level political experience, absence of track record in farming or environmental areas and ideological approach to policy are all cited as fears. However, her junior ministers are viewed more favourably in terms of tackling the enormous challenges faced by her department.

The Department of Environment, Food and Rural Affairs (Defra) is one of the ministries that will feel the greatest impact from Brexit. It has a very wide brief - from farming to fishing to floods and from pollution to protection of the natural world - the vast majority of which are currently governed by EU rules.

Leadsom, who is taking on her first cabinet role, is a supporter of “reducing burdensome EU red-tape, saving farmers time and making food cheaper” and in 2007 argued that farming “subsidies must be abolished”.

“It was very bad day for the environment when Leadsom was appointed secretary of state,” said Tom Burke, at green thinktank E3G and adviser to three previous Conservative environment secretaries. “She has no instincts for it and no knowledge of it. All her instincts are that it gets in the way of the economy and she will want to remove all those things. It really is putting a fox in charge of the hen house.”

“She also doesn’t have a lot of experience and these are complex issues that require a lot of nuance and balancing of conflicting interests,” Burke said.

Most of the major farming and environmental groups need to develop a working relationship with Leadsom and are unwilling to speak publicly of their concerns, but senior figures were extremely critical of her track record and her performance during the referendum campaign and subsequent Tory leadership contest. A common concern was that she will take an ideological approach to the brief.

However, Stanley Johnson, a former Conservative MEP and co-chair of Environmentalists for Europe (E4E), which campaigned against Brexit, said: “I have absolutely no reason not to imagine that she will be a first-rate secretary of state.”

He said lack of a track record on Defra issues need not be a problem: “That’s what all ministers are meant to be able to do, to pick up on the background.”

He said E4E “will be absolutely concerned to ensure that the substance of the environmental achievements that have been put in place during Britain’s 40-year membership of the EC and EU will be retained as far as conceivably possible.”

Owen Paterson, a previous Tory environment secretary, said he wished Leadsom well but did not wish to comment further. Caroline Spelman, Paterson’s predecessor in the role, said: “Having worked in the agricultural industry before entering parliament, I was lucky to possess some prior knowledge of how to tackle these problems, but I soon realised that I also needed to draw upon the wealth of knowledge and expertise that exists within the department.”

Spelman said: “Currently, around 80% of the UK’s environmental legislation has been set and is regulated through our membership of the EU - much to the benefit of Defra’s partners. Therefore, I would urge Andrea to engage with these organisations, as well as our international colleagues, at the earliest opportunity. I wish her good luck in her new role.”

John Sauven, Greenpeace executive director, said: “Andrea Leadsom will be responsible for the safety of the food we eat, the water we drink and the air we breathe. Her advisers at the late Department of Energy and Climate Change were able to persuade her that climate change was a real threat. We hope that she’ll be an equally fast learner when her new advisers give her the talk about the necessity of protecting our birds and the bees.”

Defra’s junior ministerial appointments have been more warmly received. George Eustice, who campaigned to leave the EU, has been reappointed as farming minister. He alarmed environmentalists in May by saying that Brexit would see the end of “spirit-crushing” EU directives that protect habitats and birds habitats.

But, after frequent changes in that post, the senior farming figure told the Guardian: “What is reassuring is that there has been some continuity with Eustice.” The senior environmentalist said: “He does strategy and detail, which is rare and he does know agriculture, which is important. But he has to renegotiate the common fisheries policy, so good luck to him.”

Thérèse Coffey, a member of the Free Enterprise Group of Tory MPs and who voted in favour of the ill-fated attempt to sell off the nation’s public forests in 2011, replaces Rory Stewart as environment minister. “I have always been impressed with her,” said the farming figure. “She strikes me as a very thoughtful, sensible and pragmatic.” Coffey campaigned to remain in the EU.

Burke said Defra was going to be a very difficult ministry to run during forthcoming Brexit negotiations. “The [Brexiteers] have made enormous promises about the environment and farming that are going to be very difficult to meet. The idea that the Treasury is going to let the farming community keep the money it currently gets from the EU is la-la land. Defra is going to be at the front in terms of broken promises.”

Leadsom is unlikely to achieve one policy she backed while campaigning for the Conservative leadership: the repeal of the ban on fox hunting with dogs. “There is no way that is going to get through the House of Commons,” said to one former environment minister.