By James Davey LONDON (Reuters) – Debenhams , Britain's No. 2 department store group, said on Thursday a volatile trading climate and unhelpful spring weather contributed to a slowdown in third quarter sales growth, which fell-short of analysts' forecasts. The company, like many other British retailers, is finding the going tough as consumers, whose spending generates about two thirds of Britain's gross domestic product, fret over job security and a squeeze on incomes. …