(Reuters) - UK shares inched higher in thin trading on Thursday as Britons begin casting their votes in a general election that could decide the fate of Brexit.The FTSE 100 added 0.3% by 0809 GMT, boosted by financial stocks and miners, though a stronger sterling hit exporters such as British American Tobacco and capped gains.The more domestically-inclined FTSE 250 advanced 0.2%, while infrastructure firm John Laing underperformed with a near 8% drop after saying it expects annual net asset..