Partners Andrews Aldridge involved using Co-op milkmen in the campaign to deliver an empty milk bottle with a note inside targeted at prospect households on their rounds.
The judges said they were impressed that the piece was more effective than any other media used in the marketing campaign, including TV advertising.
Marc Nohr, the Awards chairman and former managing director of the Lion Agency, said: "With a 26% increase on the rounds that employed the door-drop and a cost per response of less than 49p per new customer, the milk bottle door-drop is a brilliant argument as to why direct marketing can be so effective."
In total, 27 Golds were awarded this year, with a handful of agencies winning in a number of categories. These include Archibold Ingall Stretton for Skoda, which won six awards; and Leonardo London for Voluntary Service Overseas, which took home four awards.
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