Peel, core and quarter the apples, then cut into large chunks.Put into a large baking dish and toss gently with the sugar and blackberries.
Rub the butter into the flour with your fingertips or use a food processor. When the mixture resembles coarse breadcrumbs, stir in the sugar.
Tip the crumble over the fruit. Bake in a preheated oven 200 C Gas 6 for 20 mins then reduce heat to 180 C Gas 5 and cook for a further 30 minutes until the crumble is golden and the juices are bubbling through.