(Reuters) - UK blue-chip shares fell back to six-week lows on Thursday, pressured by renewed trade tensions between the United States and China, while insurer RSA advanced after a trading update. The FTSE 100, which draws more than two-thirds of its earnings from abroad, was 0.5 percent lower by 0723 GMT. The midcaps gave up 0.6 percent. Industrials, miners and Asia-exposed stocks led the fall on the main index after U.S. President Donald Trump accused China of breaking the deal they had reached..