UPDATE 1-First LNG cargo from new U.S. plant does U-turn for Britain

(Recasts throughout) LONDON, March 15 (Reuters) - The first liquefied natural gas (LNG) cargo exported from a new plant in the United States at Cove Point will arrive in Britain later this month as Asian spot LNG prices weaken relative to European benchmarks. The Gemmata tanker is expected to arrive at the UK's Dragon terminal on March 20, according to the local port authority at Milford Haven. As Asian spot LNG prices weakened, the tanker performed a U-turn in the middle of the Atl