No. 3 Gin refers to the address of Berry Bros. & Rudd, who own the recipe for the gin that is meant to be the "last word in gin for dry martinis" and are responsible for bottling. It is a traditional recipe with Italian juniper, Spanish orange zest, grapefruit zest, angelica root, Moroccan coriander, and cardamon.
At this time, we don't know who actually distills the gin for Berry Bros & Rudd.
The 2013 Wine Enthusiast review (Kara Newman) found it particularly "well suited for making gin and tonics."
In their 2011 review, the Beverage Testing Institute called it a "A fantastically flavorful and approachable nouveau gin."