Rachel allen's blackberry and apple crumble

Ingredients

• 4 large cooking Apples peeled, cored and cut into big chunks
• 1 tablespoons water
• 3 tablspoons sugar
• 225 g fresh or frozen Blackberries, or mixed berries

For the crumble:

• 170 g plain flour
• 75 g Butter
• 75 g demerara sugar