U.K. companies that get foreign investment are twice as productive as other firms, according to a new analysis that may fuel the debate over leaving the European Union. Output per worker has flat-lined since the financial crisis and some say Brexit will make matters worse by discouraging overseas investors that bring productivity-enhancing innovation, skills and technology. The Office for National Statistics said the superior performance of FDI recipients may also reflect the fact that such investment “tends to flow into the most successful businesses.”