Two of Europe’s biggest oil companies have vowed to fight two legal cases brought by environmental campaigners against their plans to develop new oil and gas projects in the North Sea.

Shell and Equinor have said that they will defend their plans to develop new North Sea projects despite Labour’s decision to withdraw government support for the plans, which were approved by the Conservatives over the last two years.

Greenpeace called for a judicial review of the government’s go-ahead for the Jackdaw gasfield, operated by Shell, which received approval in 2022. It also, alongside the campaign group Uplift, called for a judicial review of Equinor’s plan to develop a giant oilfield at Rosebank, which was approved last year.

The green groups’ campaign against new North Sea oil and gas projects received a boost earlier this week after Ed Miliband, the energy secretary, withdrew government support for the companies’ plans. Miliband has also ruled out further licensing rounds for new projects in the North Sea.

The government’s decision came months after a supreme court ruling, known as the Finch ruling, appeared to lend support to judicial reviews by finding in a separate case that the full emissions impact of burning fossil fuels should be taken into account before approving new oil and gas projects.

A Shell spokesperson said: “We accept the UK supreme court’s ruling in the Finch case, but will argue that Jackdaw is a vital project for UK energy security that is already well under way. Stopping the work is a highly complex process, with significant technical and safety issues now that infrastructure is in place and drilling has started in the North Sea.

“Jackdaw will provide fuel for UK customers – enough to heat 1.4m homes – strengthening energy independence for Britain, as other, older gas fields reach the end of production.”

Shell’s claims are rejected by campaigners, including Greenpeace. Mel Evans, a climate team leader at Greenpeace UK, said: “Rosebank and Jackdaw will do nothing to help our energy security or bring down our bills; the oil and gas extracted will be sold on the international market, making Equinor and Shell further billions in profits.

“Both the government and the supreme court agree that you cannot ignore the emissions generated from burning fossil fuels. But Shell and Equinor are trying to hide this harm they’re doing to the planet.

“Equinor and Shell know that the consents for these fields are unlawful, but despite this, they say they will continue to develop them during this judicial review, putting people and the planet at risk.”

A spokesperson for Equinor said Rosebank “is a vital project for the UK in terms of investment, job creation and energy security”.