International Paper said it would seek a secondary London listing as part of its $7 billion plan to buy British packaging peer DS Smith, as the U.S firm prepares to tussle with rival UK suitor Mondi in a potential bidding war. A London listing of the company, which has a standalone market value of about $13.53 billion, would be a boost for the British bourse, which has seen several firms leave the index, partly due to strategic and take-private deals. …International Paper last month made a proposal that valued the UK firm at 5.72 billion pounds, higher than the 5.14 billion pound deal that DS Smith agreed in principle with Mondi in early March. The U.S.-listed paper company has yet to make a firm offer for DS Smith. Both the bidders have until April 23 to make a firm offer or walk away.