Peel the apples and cut them into small pieces, then rinse the blackberries and put all the fruit into a saucepan with the water and a sprinkling of sugar to sweeten. Leave the fruit to gently cook on medium heat whilst you prepare the crumble topping.
Pre-heat the oven to 200 C / Gas 6.
Begin by measuring the flour and margarine into a large bowl and rub together to form breadcrumbs. Then stir in the sugar and oats.
Now that the fruit has softened, drain out the majority of the water but leave some in the pan. Then transfer the contents of the pan into a medium-sized oven dish and spoon the crumble topping on top.
Bake the crumble for 30 to 35 minutes, or until golden brown and the fruit is bubbling. Serve warm with cream, ice cream or custard. Enjoy!