Next time you're in Woolworth's or Blockbuster, look out for publicity inviting you or your pupils to become Dubble Agents. Dubble chocolate bars are produced according to fair trade agreements, guaranteeing producers a social premium to help pay for schools and clean water. Dubble Agents will receive a number of "secret missions", such as organising petitions to persuade the school shop to stock fair-trade products or meeting Ghanaian cocoa farmers and sharing the experience with local newspapers. They'll also get more conventional items such as badges, membership cards and - to keep things sweet - a Dubble bar. Information about Dubble Agents is available in many shops where Dubble bars are sold. To register as a Dubble Agent and to download education materials, visit the website.