Which of the following malts is primarily used to produce nutty British ales?

Biscuit malt is primarily used in the production of nutty British ales due to its unique flavor profile and toasty characteristics. This malt is kilned at a relatively high temperature, which develops flavors reminiscent of toasted bread, biscuits, or cookies. These qualities contribute to the rich, nutty, and slightly sweet character typical of traditional British ales, making it a favorite among brewers aiming for those specific flavor notes.

Amber malt also has a toasty and nutty character but is not as commonly used as Biscuit malt in these styles. Pilsner malt is more associated with lighter, crisp beer styles like lagers and does not impart the same nutty qualities. Caramel malt provides sweetness and body but generally contributes to flavors of caramel or toffee rather than a nutty profile. Thus, Biscuit malt stands out as the primary choice for achieving the sought-after nutty flavor in British ales.