By Jon Robinson A court case over equal pay involving more than 60,000 Asda workers has started amid demonstrations being staged in Brighton and Manchester. The GMB union, which has said the case is the biggest ever in the private sector, is arguing that the predominantly female retail workforce is paid up to £3.74 an hour less than the mainly male warehouse workforce and that shop floor work should be of equal value to warehouse work. Workers demonstrated outside the TUC Congress in Brighton and in Manchester where the case is being held. As the hearing began Andrew Short KC, representing the…