Transport secretary Grant Shapps 'overrode' official advice to review the £27.5bn Road Investment Strategy 2 (RIS 2) on environmental grounds, according to reports.
It has been a legal requirement to take into account the environmental impact of such major infrastructure projects since 2014.
Lawyers for the campaign group Transport Action Network (TAN) have argued for a judicial review of RIS 2 on climate impact grounds, and plan a separate but connected legal case over the 2014 National Policy Statement for National Networks (NPS).
TAN states: 'We're challenging the Government's refusal to review the national policy that governs planning approval for new roads (National Policy Statement for National Networks) (NPS). Currently it doesn't allow decision makers to seriously consider climate change.'
According to reports in the Guardian, High Court filings in the case show evidence Mr Shapps decided to override Whitehall advice to review the 2014 NPS.
The details are set out in court papers that form part of a legal challenge to the policy.
A submission from David Wolfe QC states: 'On the day before the limitation period for issuing this challenge was due to expire, the defendant provided the claimant with the advice of his officials, which was that it was appropriate to review the NPS.
'The claimants have been presented, on the one hand, with official reasoning in support of a review, and on the other, with a decision by the defendant not to review the NPS, with no explanation of why, or on the basis of what information or considerations, he chose to depart from his officials’ advice.'
Government lawyers argue the transport secretary has no duty to provide reasons for his decision and say the claim is baseless.
They also argue that despite policy changes since 2014, the RIS 2 'would not have been materially different if the changes had been anticipated'.