The US ambassador to the UK has warned Britain’s sky-high energy prices threaten to undermine its status as a major global economy. Speaking at an event at the Savoy Hotel on Wednesday, Warren Stephens described UK energy prices, which are among the highest in the world, as the “chief obstacle” to growth. “Energy costs in the United Kingdom are too high on which to run an industrialized economy,” Stephens said. “Every business I meet, in every sector, complains to me that energy costs make the UK an expensive,…