British fashion house Burberry warned that trading conditions were becoming more challenging with like-for-like sales flat in the second quarter.The firm said that ahead of the key retail trading period in the second half, it expected pre-tax profits for the year to 31 March 2013 to be at the lower end of market expectations. The company, which had been riding on the crest of a retail wave driven by it popularity in the Far East, said retail sales growth at constant exchange rates was 6% in the 10 weeks to 8 September. Of this, new space contributed the whole 6% while like-for-like store turnover was unchanged year-on-year, with sales slowing in recent weeks. Chief Executive Angela Ahrendts, said the second quarter retail sales growth had slowed against historically high comparatives. "Given this background, we are tightly managing discretionary costs and taking appropriate actions to protect short term profitability, while continuing to execute on our proven five key strategies," she said.