RETAILER JD Sports Fashion posted a hike in sales today, but warned that maintaining profit margins "may prove increasingly challenging" as result of the weak pound.The board of Bury-based company, one of the star performers on the High Street, said that despite the concerns over margins it remained "encouraged" by the progress made so far this year.JD Sports Fashion operates the JD Sports and Bank retail brands. Last month it dipped its toe in the water of  the Continent with the acquisition of French fashion footwear chain ......for the full story register now for free or login below...