The three agencies will now work together on an integrated launch strategy for Tate & Lyle's Light Cane product, a low-calorie sugar alternative that will go on sale nationally in September.
Hall Moore CHI will create a loyalty scheme and maintain the brand's online activity, while Naked Inside will take charge of media planning.
Media buying, however, remains with MediaVest Leeds.
Julia Clark, the marketing manager at Tate & Lyle, said: "The team approach offered to me by the CHI Group has already demonstrated how much of a difference it can make to the creativity of our communications."
Tate & Lyle is the second-largest player in the £268 million UK sugar market, with a market value of £54 million.
The company appointed CHI to its £3 million advertising account in January following a three-way pitch.
Tate & Lyle becomes the third account to employ CHI on a group basis, following the examples of the Royal Bank of Scotland and The Carphone Warehouse.