The judge's ruling has set some firm boundaries for the Government's future actions.
Campaigners who fear that environmental protections will be weakened after Brexit have lost a High Court fight but said a judge has set "firm boundaries" for ministers.
Charity ClientEarth and the Marine Conservation Society are worried about aspects of regulations relating to conservation of habitats and species which will come into force when the UK leaves the European Union.
They say new powers will allow ministers to alter and reduce standards for protected sites.
A High Court judge on Thursday blocked their bid for a judicial review after analysing argument at a hearing in London.
Mrs Justice Lieven concluded that the two organisations had no chance of winning at a trial and refused to allow their claim to proceed.
But ClientEarth said her ruling nevertheless makes it "clear" that any future decision will be open to challenge.
"We would have liked to have seen this case go ahead; however, the judge's ruling has set some firm boundaries for the Government's future actions," said a ClientEarth spokesman.
"The court has made it clear that any future decision based on the regulations would be open to challenge and that special conservation sites for wildlife and habitats should not be reduced or removed without going through full and proper scrutiny."
He added: "The public can be sure that we will be monitoring the Government's decisions and will take action if we think it's needed."
Mrs Justice Lieven was told that regulations had been put in place to replace current European rules.
Lawyers representing Environment Secretary Theresa Villiers disputed complaints by ClientEarth and the Marine Conservation Society and said she had "expressly committed" to "not weakening"environmental protections when the UK left the EU.
Chris Tuckett, director of programmes at the Marine Conservation Society, said: "This case was about ensuring that the legal protections in place now to protect our most precious habitats and species are not weakened post-Brexit.
"The specific changes to legislation that we challenged present a real risk that protected areas on land and at sea will not be secured for future generations."
Brian Farmer is a reporter with PA.