The CEOs of major U.K. retailers, including J Sainsbury and Tesco, have warned that uncertainty over the future of customs for shipping food into Northern Ireland “could force many retailers to move supply chains from GB to the EU”. The U.K. government will shortly be making a proposal to adapt the Northern Ireland Protocol ahead of a Sept. 30 deadline for imposing stricter customs rules. Shipments of food to Northern Ireland from the Republic of Ireland were worth 69.5 million euros ($81.9 million) on average in the first five months of 2021, equal to 27.5% of all exports. U.K.-EU trade...