A new legal challenge is being launched today against the Government's controversial high-speed rail project HS2.
The HS2 Action Alliance (HS2AA) is joining Hillingdon Council in west London to accuse the Transport Secretary of unlawfully issuing "safeguarding" directions without first undertaking a strategic environmental assessment.
The directions are aimed at preventing construction work which might interfere with the project.
The campaigners say a successful challenge before Mr Justice Lindblom at London's High Court would lead to the current ban on developing land along the proposed route of Phase 1 of the project being lifted.
They say the ban could not be reinstated until the Government has completed a valid environmental assessment.
Hillingdon Council leader Ray Puddifoot said: "Despite the Government telling us that resistance is futile, we will continue our fight against this flawed plan, however long it takes.
"This is not a done deal and we will continue to challenge the Government.
"We also remain committed to assisting residents groups and local businesses and will continue to help wherever possible with the resources and support people need."
HS2AA director Hilary Wharf said: "Since the start of this project there has been a sorry story of the Government trying to avoid important environmental protection requirements which are enshrined in law.
"We believe that the same environmental and planning law standards should apply to HS2 as any other project, and we are prepared to go to the High Court to protect that principle".
A Department for Transport spokesman said: "HS2 is a vital part of the Government's long term economic plan and we are determined to ensure Britain will benefit from the jobs, skills and extra capacity it will provide.
"We are confident that the decisions on HS2 have been taken lawfully and fairly and are vigorously defending this legal challenge."
"Attempts to obstruct HS2 have already been firmly rejected by three courts and we are very confident that this latest claim will not succeed.
"We will continue to drive work forward to ensure that the benefits of HS2 can be realised as soon as possible and in line with our legal obligations."
Hillingdon Council fears the loss of important amenities and massive disruption to traffic and business over many years if building HS2 - currently expected to cost £42.6bn for the project and another £7.5 billion for trains - goes ahead.
Its leaders are warning that a new landfill area would be created next to thousands of homes and become one of Europe's largest, while an outdoor activity centre would be lost, along with numerous wildlife sites.