By Karlee Weinmann ( March 18, 2013, 5:18 PM EDT) -- Despite earlier reports, a source told Reuters on Monday that Qatar Holding LLC is not mulling an £ 8 billion ($12 billion) takeover of British clothing retailer Marks & Spencer Group PLC. The U.K. company's shares soared on news that a multibillion-dollar buyout could be in the works, a prospect first suggested by a weekend piece in The Sunday Times. If the Qatari sovereign wealth fund and a consortium of other Middle Eastern investors had pursued a deal, as outlined by The Sunday Times, it would have been the heftiest private equity buyout of a British company since KKR & Co. LP coughed up £11 billion for drug store chain Alliance Boots GmbH....