Channel 5’s new owner is talking to rivals, including Channel 4 and UKTV, about a possible advertising sales alliance as the broadcaster struggles to overcome a boycott by Omnicom Media Group over a pricing dispute which began last July, before Viacom bought the channel. The boycott is estimated to be costing the broadcaster as much as GBP50 million a year in lost revenue, or about 15% of turnover, as the agency’s clients, which include Boots, Sony and McDonald’s, switch to bigger broadcasters such as ITV.