Preheat the oven to 180 degrees C. Grease a 12 cup muffin tray or line with patty cups / muffin cases.
In a large bowl stir together the plain flour, wholemeal flour, sugar, oat bran, quick-cooking oats, wheat germ, baking powder, bi carb soda and salt. Gently stir in the blueberries and walnuts. In a separate bowl mix together the mashed banana, buttermilk, egg, oil and vanilla. Pour the wet ingredients into the dry and mix just until blended. Spoon into muffin cups filling all the way to the top.
Bake for 15 to 18 minutes in the preheated oven or until the tops of the muffins spring back when lightly touched.