Preheat oven to 180°C (355°F). Line a 12-hole muffin pan with paper muffin cases. Sift flour, cocoa and bicarbonate of soda into a large bowl. Stir in sugar and chocolate bits and make a well in the centre. In a small bowl, use a fork to whisk together margarine, milk and egg, then add to flour mixture. Stir gently until mixture is just combined (do not over-beat). Fold raspberries into the mixture. Spoon mixture into cases. Bake for 20-25 minutes or until muffins are well risen and spring back to the touch. Leave in pan for a few minutes, then transfer to a wire rack to cool.