The billionaire Barclay brothers, who live on Brecqhou, have lost a battle with the UK's HM Revenue and Customs after the Supreme Court ruled that the taxman does not owe them £1.25 billion.
Sir David and Sir Frederick Barclay had been pursuing the claim after Littlewoods, the retailer they own through Shop Direct, overpaid VAT to HMRC between 1973 and 2004.
The company had already received a £205 million refund from HMRC, together with "simple interest" of £268 million.
But Littlewoods has been seeking "additional interest" calculated on a compound basis amounting to £1.25 billion on the grounds of the "common law of restitution, either as restitution for a mistake of law, or as restitution of tax unlawfully demanded".
However, the Supreme Court unanimously dismissed the claim.