It is understood that Harris declined Central Office's request for him to commit to the role for a further year. He will continue in the short-term to act as an unpaid consultant to the party -- which will announce a significant revamp to its famous torch logo at the end of this month -- before seeking a return to the commercial arena.
Harris was the brains behind the Tory's "Let Down by Labour" ads for the recent local and European election campaign. He also devised a competition inviting the advertising community and the public to create an ad for the party. But his innovations have not helped lift the Tories from its mediocre showing in the opinion polls.
Harris gets married later this week and plans to finish his book on the phenomenon of text messaging when he returns from his honeymoon next month.
"I'm proud of my achievements over the past nine months but I'm looking for something new and exciting to do elsewhere," Harris said. "My future is in the commercial world not the political world."
Howard appointed Harris alongside party co-chairman Maurice Saatchi and press secretary Guy Black after he won the party leadership last autumn.
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