HS2 Ltd, the government-owned company tasked with delivering the HS2 project, wants to erect fencing and an earth embankment in a field near South Harefield to enable protected great crested newts to be relocated out of the way of a proposed viaduct to carry trains across the Colne Valley.
The company had deemed permission to carry out the works under the High Speed Rail (London-West Midlands) Act 2017 but was required to seek the London Borough of Hillingdon's approval of its detailed plans and specifications of the proposed works.
The site, which is immediately north of the Chiltern Main Line and about 1.1 kilometres from South Harefield, is within the Colne Valley Archaeological Protection Zone. A third of it is also within the Mid Colne Valley Site of Importance for Nature Conservation.
Hillingdon Council refused to grant approval on the basis that the design and external appearance of the works should be modified to preserve a site of archaeological interest and nature conservation value. It said the development could reasonably be carried out elsewhere.
HS2 Ltd asserted that it would investigate the potential impact of the works upon any archaeological remains and take all necessary mitigation and modification steps.
A planning inspector later agreed with the council, but the secretaries of state for transport and housing, communities and local government went their own way last year, upholding the company's appeal.
Hillingdon Council's challenge to that decision was subsequently rejected by a High Court judge. However, the local authority has now won its appeal against the judge's ruling.
The case hinged on the interpretation of schedule 17 of the HS2 Act, which created a new planning regime for the approval of certain matters relating to the design and construction of the railway, and the agreement between the government and HS2 Ltd as the project's nominated undertaker.
Ruling in Hillingdon Council's favour on the issue, the appeal judges concluded: "The duty to perform an assessment of impact, and possible mitigation and modification measures under schedule 17, has been imposed by Parliament squarely and exclusively upon the local planning authority.
"It cannot be circumvented by the contractor taking upon itself the role of conducting some non-statutory investigation into impact.
"We have also concluded that a local planning authority is under no duty to process a request for approval from HS2 Ltd unless it is accompanied by evidence and information adequate and sufficient to enable the authority to perform its statutory duty."
The court added: "Parliament intended local planning authorities and HS2 Ltd to work in an effective and collaborative way that balances important local interests with the broader national interest in the delivery of the HS2 project, to which the government is committed and which Parliament has approved.
"The object of this cooperation is to prevent the planning process creating an undue hindrance to achieving the broader national interest while giving proper weight to local concerns. The court's judgment is consistent with that important aim."
Lord Justices Lindblom, Haddon-Cave and Green sent the issue of whether approval should be granted for the works back to the secretaries of state for fresh consideration in the light of their ruling.
The court also ruled on very different issues raised by environmental campaigner and TV presenter Chris Packham in a separate challenge to Prime Minister Boris Johnson's announcement in February that the HS2 project would proceed.
Johnson reached that decision after an independent review chaired by Douglas Oakervee, a civil engineer who is a past chairman of both HS2 and Crossrail. Packham argued that the government had misunderstood local environmental concerns and failed to properly examine the environmental effects of the high-speed link.
He said that no account had been taken of the project's impact on greenhouse gas emissions between now and 2050 in light of the government's obligations under the Paris Agreement and the Climate Change Act 2008.
Packham argued that the Paris Agreement was "obviously material" to the Prime Minister's decision and that greenhouse gases generated by HS2's construction would clearly impact on the UK's legal commitments to attain net zero carbon emissions by 2050.
But Packham's judicial review application was dismissed as unarguable by a judge and the Court of Appeal last week rejected his appeal against that conclusion. It was "not properly arguable" that the government had misled itself or been misled into thinking that the Oakervee review contained a full assessment of the project's environmental effects, it found.
The court concluded: "There is nothing to show that the government either ignored or misunderstood the legal implications of proceeding with HS2 for its obligations relating to climate change, including those arising from the Paris Agreement and under the provisions of the Climate Change Act."
R on the Application of London Borough of Hillingdon Council v Secretary of State for Transport & Anr. Case Number: C1/2020/0152
R on the Application of Packham v Secretary of State for Transport & Anr. Case Number: C1/2020/0682