The drinks giant intends to back the September launch with a £2m advertising campaign that will include national print, outdoor and direct activity.
Slate 20, which is flavoured with lime and ginger, will be aimed at 20- to 30-year-old men seeking an alternative to beer with a more masculine image than other RTDs.
The 4.5% abv brand will be available exclusively via the on-trade, priced between £2.50 and £3.30 a bottle.
Slate 20 will be sold only in the UK, though mother brand Slate Blended Bourbon is already sold in Australia. Diageo is evaluating whether or not to launch the latter in the UK.
Diageo's RTD portfolio includes Smirnoff Ice and Archers.
The RTD sector declined nearly 20% in the 12 months to March 2005, according to ACNielsen.
Lavinia Leung, innovation manager at Diageo GB, said: "The RTD sub-category continues to provide a strong platform for new innovations.
"Although the overall category is in decline strong brands continue to perform ahead of the category. Diageo GB will continue to develop innovations to drive category growth."
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