Advertising agency WPP has reportedly teamed up with private equity firm General Atlantic to bid for Tesco's loyalty card business, Dunnhumby.According to Bloomberg, the two firms are among those who submitted offers last week for the business. It cited people familiar with the matter as saying that other bidders include Advent International and Warburg Pincus. Permira Advisers, which may team up with Google, also bid, they said.Tesco hired Goldman Sachs to explore options for Dunnhumby, including a sale, in January. The original £2bn price tag has since been cut to closer to £1bn due on concerns that once the operation is no longer part of Tesco it will be less attractive to clients such as Coca Cola, people close to the matter told Bloomberg.