The Department for Transport’s £27 billion road development scheme is unlawful after the Government ignored its impact on climate change, the High Court has heard.

In March 2020, the Department for Transport (DfT) set out its Road Investment Strategy 2 (RIS2) for major roads in England from April 2020 to March 2025.

The strategy is made up of 50 major road schemes, including controversial plans for the A303 Stonehenge tunnel and the Lower Thames Crossing linking Kent and Essex.

The Transport Action Network (Tan), which supports sustainable transport campaigns, has accused Transport Secretary Grant Shapps and the DfT of unlawfully failing to take account of the “obviously material” impact of RIS2 on achieving climate change objectives.

At the High Court on Tuesday, Tan argued the Government failed to consider commitments to tackle climate change, made up of the use of carbon budgets and the legally binding target to cut emissions to net-zero by 2050.

It also failed to consider its objective following the terms of the Paris Agreement, which commits signatories such as the UK to tackle climate change by taking measures to limit global warming to well below 2C, the group said.

David Wolfe QC, for Tan, told the High Court in written arguments: “RIS2 is a major roads programme.

“It also provides for traffic growth.

“Its impacts on climate change generally, and the three climate objectives in particular, were obviously material to the setting of RIS2.”

The barrister said it was “plainly material” for DfT to consider the impact on climate change given that the RIS2 would increase greenhouse gas emissions and that road transport is a “significant and familiar” source.

Mr Wolfe continued: “The claimant is not saying that a policy or a development is inevitably unlawful if it increases greenhouse gas emissions.

“It is that an analysis of the significance of an increase in emissions must grapple with the fact that any increase is undesirable, given the pressing need for emissions to decrease.”

He added: “Unless and until all road vehicles, their manufacture and servicing, the power generated to propel them – including construction of additional renewable electricity capacity – road operation and maintenance are all zero-emission… an increase in road traffic means an increase in greenhouse gas emissions.

“In that respect, RIS2 inevitably has an undesirable impact on the climate and thus the environment.

“The Secretary of State needed to grapple with that.

“He could not just ignore it, as he did.”

The DfT is disputing the claim.

John Litton QC, for the department, said it was obliged to have regard to the effect of the strategy on the environment when setting RIS2.

However, he said the law did not oblige DfT to expressly consider the climate objectives, arguing Tan’s complaint was with how the considerations were made.

He said in written arguments: “It is not accepted that the climate objectives were so obviously material to the decision to set RIS2 that the defendant was legally obliged to take them into account.

“Instead, these were considerations which the defendant was able, as a matter of discretion, to consider and take into account.”

Mr Litton continued to say that the development of RIS2 did consider the net-zero target and was informed by analysis that undertook an estimation of the potential carbon impacts.

“RIS2 makes multiple references to its potential effects on the environment and to the need specifically to achieve decarbonisation of the transport network,” the barrister added.

The barrister later said there was a difference of expert opinion as to how the comparative impact of RIS2 should be considered, and that the project will “bring enormous wider benefits that will be in the public interest”.

He concluded: “The defendant had full and proper regard to the environment when setting RIS2, including to climate change-related impacts on the environment and carbon emissions in particular, consistent with the Government’s climate change responsibilities.”

The case before Mr Justice Holgate is due to conclude on Wednesday with judgment expected to be reserved until a later date.