WPP is preparing to lock horns with Bain Capital in Tokyo, after the Boston-based private equity firm launched a $1.3bn tender offer for Japan’s third-biggest advertising agency — a long-term business partner of the UK-listed giant. Just hours after Bain’s offer was made public, people close to WPP said on Monday night that it did not intend to sell its 24.7 per cent stake in Asatsu-DK (ADK) at the ¥3,660 price offered by Bain, as the tender “severely undervalues” the Japanese firm.