The Government may face a legal challenge to its £33 billion HS2 high-speed rail project, it was revealed today.
Opponents of the scheme are also contacting the European Commission over concerns about HS2's environmental impact.
Last month Transport Secretary Justine Greening signalled a go-ahead for HS2, whose first phase will see a new high-speed line, crossing through Tory heartlands, from London to Birmingham.
Today, HS2 Action Alliance (HS2AA) wrote to Ms Greening asking her to abandon the scheme and giving her notice that the alliance could challenge her decision through judicial review.
The alliance said the grounds for the legal challenge were "the failure of the Department for Transport (DfT) to comply with the legally binding requirements of the Strategic Environmental Assessment (SEA) Regulations 2004 and the Conservation of Habitats and Species Regulations 2010".
HS2AA added that the SEA regulations required a full strategic environmental assessment of any important infrastructure project and an assessment of all alternatives to be completed before any proposals are presented for public consultation.
It said the Government had failed to do this with HS2.
A separate letter of complaint regarding the UK Government's "non-compliance with the SEA directive" was also sent today to the EC, "inviting the commission to investigate the actions of the UK Government on this matter".
HS2AA said its letter to Ms Greening was supported by four wildlife trusts along the route, and more than 70 action groups and resident associations affiliated to HS2AA.
An HS2AA spokesman said: "HS2 is an environmental disaster for our country.
"It will irreversibly damage many landscapes, ancient woodlands and wildlife habitats which simply cannot be replaced. It will also do nothing to reduce carbon emissions.
"If the Government is determined to push such a scheme, the economic justification should be overwhelming, but this simply isn't the case.
"Figures buried by the Department for Transport on January 10, the announcement day, indicated that the already shaky business case put forward to justify HS2 is now virtually non-existent."
The spokesman went on: "The DfT and HS2 Ltd have ridden rough shod over public opinion and many expert voices to ignore all viable alternatives in their desperation to promote HS2. We are still hopeful that Justine Greening will see sense and halt a project which offers such limited benefit for so much environmental damage.
"If the Government had done the assessment properly they simply would not have reached the conclusion they did."