Friends of the Earth, ClientEarth and the Good Law Project took legal action last year over carbon budgets set by the government in 2023 to meet Britain’s target of net zero by 2050.

Those emissions targets were set after a 2022 ruling that Britain had breached legislation designed to help reach the 2015 Paris Agreement goal of containing temperatures within 1.5 degrees Celsius of pre-industrial levels.

The three groups argued that the new plan was also unlawful, citing as one example the fact that the then energy minister Grant Shapps was not told of the risk that policies to reduce emissions could not be delivered.

Judge Clive Sheldon upheld four out of five grounds of their legal challenge in a written ruling on Friday.

Friends of the Earth’s lawyer David Wolfe said Britain’s Climate Change Committee warned last year there were credible policies in place for less than 20% of the reductions required to meet the carbon budget for the period 2033-2037.

But, the group said, Shapps “proceeded on the assumption that the reductions in emissions of greenhouse gases from all of the proposals and policies … would all be delivered in full”.

Lawyers representing the Department for Energy Security and Net Zero said Shapps did not assume emission reductions would be delivered in full.

But the High Court ruled that Shapps was wrongly told by officials that “each of the individual proposals and policies that form the package of measures would be delivered in full”, rendering the carbon budget delivery plan unlawful.

(Reporting by Sam Tobin)