The National Trust, RSPB and Wildlife Trusts say all options are on the table amid a rural revolt.
Three UK conservation groups say all options are on the table as they challenge what they describe as a government U-turn on protecting nature.
The National Trust, RSPB and Wildlife Trusts said they could urge millions of members to take to the streets in demonstrations.
The groups’ leaders said new government policy was an “attack on nature”.
The government said it was improving regulations and wildlife laws “in line with our ambitious vision”.
“A strong environment and a strong economy go hand-in-hand,” a government spokesperson said.
Hilary McGrady, who runs the National Trust; the chief executive of the Wildlife Trusts, Craig Bennett; and Beccy Speight from the RSPB made their comments in a joint interview with the BBC.
They all heavily criticised the government over what they call its “U-turn” on Conservative manifesto promises on the environment.
Plans to scrap EU protections for nature, a relaxation of planning laws in new “investment zones”, and the review of environmental farm subsidies were all cited.
It is the first time the leaders of the three groups have formed such a high-profile and outspoken coalition on an issue in this way.
The combined membership of the three organisations is eight million, including many Conservative voters from across the country.
According to the RSPB, its members have sent 106,000 emails to MPs in two weeks.
Mrs McGrady of the National Trust said: “This is the biggest attack on nature certainly in my lifetime and let alone my career. This is unprecedented – that’s why we are stepping forward with the RSPB and Wildlife Trusts.
“We choose our battles very carefully – and we don’t do it very often.”
Mr Bennett said: “At the Wildlife Trusts we are hearing from tens of thousands of our supporters, also from huge numbers of farmers and businesses who are also concerned. This goes right across society.”
While climate action groups like Extinction Rebellion and Just Stop Oil embrace tactics like gluing themselves to roads, members of the National Trust, RSPB and Wildlife Trusts are more often associated with hiking, bird-watching or visiting stately homes than taking direct action.
But Mrs Speight of the RSPB and Mr Bennett said they would be prepared to organise a march in London if the government didn’t provide the guarantees they were seeking.
“All options are on the table in terms of what comes next,” said the RSPB head. “This is something we just can’t allow to go forward. Any campaign has lots of tools in the toolbox. We have to prepare to use as many of those tools as will be effective.”
Mrs McGrady stopped short of saying she would call out her members, but did not rule it out. She said: “We will do what the most effective thing is to do.”
She also added a warning: “At some point we will run out of patience.”
Mrs McGrady said that neither she nor Mr Bennett had been invited to meet the new Environment Secretary Ranil Jayawardena, which she said was “not normal”.
Other major organisations also voicing their anger include the Angling Trust, the Rivers Trust, the Woodland Trust, Wildlife and Countryside Link, along with numerous regional charities.
A bill passed in September means all post-Brexit laws – some 2,400 – must be reviewed or abandoned by the end of 2023. Around 570 cover aspects of the environment, from sewage pollution and pesticide use to protection for wildflower meadows and wetlands.
Department for Environment, Food and Rural Affairs (Defra) officials have privately expressed concern about whether such a mountain of legislation can be examined in such a short timeframe.
Wildlife groups also fear that protected landscapes and fragile ecosystems could be at risk from government plans to set up new investment zones with lower taxes and “liberalised” planning laws.
As many as 38 local authorities are thought to be in talks with the government over setting up the zones, with the goal of releasing more land for commercial and housing developments.
The National Trust has said the plans could create “grey zones” which are “devoid of nature or historic character in which people have no say in the development that impacts them”.
The “rapid review” of the new post-Brexit Environment Land Management Scheme (ELMS) is also provoking confusion and anger among farmers.
ELMS is designed to replace the criticised EU system, where farmers were paid based simply on how much land they had.
Instead ELMS would pay farmers for providing environmental benefits to the public, such as restoring woodland, preventing pollution from entering rivers, and working towards net zero targets.
Rural groups and farmers had contributed to its design, and many contracts for some of the larger schemes have already been drawn up.
However this has been put on hold until the results of the government review, due to be published at the end of October.
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