Reuters: An environmental activist who threw green custard at Business Secretary Peter Mandelson has been arrested and bailed, police said on Sunday. Leila Deen, 29, was arrested on Saturday and bailed to return to a central London police station in April. Deen, from environmental group Plane Stupid, threw a cup of the liquid over Mandelson as he arrived for a low-carbon industry summit in London on Friday. She attacked Mandelson because of his support for a new third runway at …