A Jersey-based oil-refining company is suing the EU, Germany and Denmark for at least €95m over a windfall tax introduced during the Ukraine war that it sees as a “pretext” for undermining fossil fuel firms, leaked documents show.

Klesch Group Holdings Limited is taking action under a controversial secret court system enabled by the energy charter treaty (ECT), an agreement officials fear will stymie climate action and divert hundreds of billions of euros into the coffers of fossil fuel investors.