Set half the raspberries aside. In a bowl, roughly mash the remaining raspberries with the sugar. Cut the Madeira loaf into 12 slices, then use a round cutter to cut out rounds of the cake to fit 4 serving glasses. Beat the clotted cream until slightly thickened.
Layer up the trifles in glasses starting with a slice of cake, then some cream and some mashed raspberries. After the final slice of cake, spread over some cream and top with whole raspberries. The trifles can be kept in the fridge for a couple of hours. Dust with a little icing sugar before serving.