Line 2 large baking sheets with nonstick baking paper.
Whisk the egg whites in a large clean bowl until they form stiff peaks. Add the sugar a spoonful at a time and continue to whisk until thick and glossy. Fold in the vinegar with a large metal spoon.
Spoon or pipe 12 meringues on to the prepared baking sheets. Place in a preheated oven, 150°C (300°F), Gas Mark 2, for 1 hour, then switch off the oven and leave the meringues to cool completely. When cool, roughly crush the meringues.
Whip the cream in a large bowl until it forms soft peaks. Roughly crush together the raspberries and strawberries and stir into the cream. Fold in the crushed meringues, icing sugar and cream liqueur. Spoon into 6 tall glasses, decorate with extra whole berries, and serve immediately.