Russian collectors and a U.K.-based diamond dealer emerged as big buyers in this month’s record-breaking London art auctions. They battled for trophies by 20th-century artists at Christie's and Sotheby's, spending about 258.9 million pounds with fees. Among the bidders was Laurence Graff, Chairman of Graff Diamonds Ltd, who bought Picasso’s 1963 painting “Tete de Femme (Jacqueline)” at Christie’s for 8.1 million pounds, double the upper estimate.