1) Preheat the oven to 200°C/ gas mark 6. Coat a 20 by 20cm baking dish with cooking spray.
2) In a large bowl, toss the berries with wholemeal flour, sugar and zest. Transfer the berry mixture to the baking dish and set aside.
3) In a medium bowl whisk together the wholemeal flour, plain flour, two tablespoons of sugar, baking powder, bicarbonate of soda and salt. Cut in the butter using two knives or a pastry cutter until many small pebble-sized pieces are formed.
4) In a small bowl or pitcher, whisk together the buttermilk and oil. Add the buttermilk-oil mixture to the dry ingredients and mix until just moistened. Do not over mix. Drop the batter onto the fruit forming 6 mounds. Sprinkle with the remaining tsp of sugar.
5) Bake for 30 minutes, until fruit is bubbly and top is golden. Let stand for at least 10 minutes before serving.