In February, Prime Minister Boris Johnson gave his backing to the HS2 project. This followed his consideration of the government-commissioned Oakervee report into the future of the scheme.
Johnson’s consent was not a planning decision - royal assent for the first phase of the HS2 scheme between London Euston to Birmingham was granted in February 2017.
A bill to deliver phase 2a of the scheme, between Birmingham and Crewe, was introduced to Parliament in 2017. The bill received its second reading in the House of Lords on 9 September 2019. A date for the committee phase of the bill has yet to be announced.
However, according to a statement from Packham’s solicitors, Leigh Day, Packham intends to halt the scheme by arguing that Johnson’s decision to give the go-ahead to HS2 was unlawful because it relied on the "flawed" Oakervee review process "and did not take into account the full environmental costs of the project".
The statement added that Packham believes that HS2 "will damage or destroy almost 700 wildlife sites, including over 100 Ancient Woodlands".
He also argues that the "climate impact of HS2 is expected to be incompatible with any net zero emissions target, not least because the line will facilitate the large-scale expansion of airports across the UK".
Packham argues that, since the initial environmental statement for HS2 phase one in 2013, the government has signed the Paris Agreement and committed to a policy of achieving net zero carbon emissions by 2050.
"In his legal case Mr Packham argues that the Prime Minister’s decision relies on the mistaken understanding that the Oakervee report had taken carbon emission impacts into account, such as the facilitation of airport growth and expansion outside of London," the Leigh Day statement said.
Last week, the government's Airports National Policy Statement (ANPS) favouring a third runway at Heathrow was declared unlawful by the Court of Appeal - because the UK's obligations to tackle climate change under the Paris Agreement were not taken into account.
Packham said: "I believe the review central to the mandate to proceed [with HS2] was seriously flawed in its methods. I believe that essential submissions regarding environmental concerns were ignored by the review panel. As a consequence, the Oakervee review is compromised, incomplete and flawed and thus the decision to proceed based upon it is unlawful."
On his crowdfunding page, Packham said he has instructed his lawyers to send a pre-action legal letter to the Prime Minister "challenging his decision and calling on him to think again." The next stage in the legal process would be to make a formal application to the High Court.
Angus Walker, partner at law firm BDB Pitmans said: "It might well be that Chris Packham senses infrastructure projects to be vulnerable given Thursday’s Heathrow decision.
"However, that was a narrow one, and the decision to allow HS2 to go ahead (which was merely a re-confirmation that it was already going ahead) does not have the same requirements as a National Policy Statement and hence less reason that it can be flawed.
"Notably, HS2 will be electric, so when electricity becomes carbon neutral the running of HS2 will too, although as noted by Mr Packham and his lawyers, that ignores construction costs and impacts."
An analysis article looking at the planning work needed for HS2 can be found here.