UPDATE 1-Sainsbury's overtakes Asda to become UK's No.2 supermarket

* Asda sales fall 2.7 pct in 12 weeks to July 19 - Kantar * Sainsbury's now No. 2 player - Kantar * Analysts say pressure mounting on Asda CEO Andy Clarke LONDON, July 28 (Reuters) - Asda, the British arm of U.S. retailer Wal-Mart, on Tuesday lost its status as Britain's No. 2 supermarket group to rival Sainsbury's as industry data confirmed it as the sector laggard. Asda's sales fell 2.7 percent over the 12 weeks to July 19, reducing its market share to 16.4 percent from 17.0