Packet lists general directions when added to plain flour.
Baking powder is a special agent that increases lift in various bakery recipes, including; bread loaves, rolls, muffins and American pancakes. Borwick's baking powder is to be used in the exact amount given in the recipe you follow. Usually you'd use baking powder in plain flour.
Baking powder is usually used instead of yeast to lift cakes and biscuits. For most recipes, mix 1-2 teaspoonfuls of baking powder per half-kilo (pound) of flour for best effect.