By Jack Mendel Beleaguered utilities firm Thames Water was dealt a fresh blow this week after a major investor cut the value of its stake by two thirds. Universities Superannuation Scheme (USS) slashed its stake in Thames Water to £364.4m from £955.8m the year before,according to official accounts published at the end of December for its Church Water Investment. USS, which holds around 20 per cent of Thames Water’s parent firm Kemble, cut down its investment by 62 per cent according to the FT, as the utilities giant faces mounting problems. The decision was “probably difficult but necessary” a…