Put flour into a large mixing bowl. Add the butter, and using finger tips, rub it into the flour until it is well mixed in. Add the sugar and the porridge oats and mix well.
To make the crumble filling:
Mix all the fruits together. Mix in sugar. Spoon into a greased pie dish, or a greased shallow ovenproof dish. Sprinkle with the crumble topping and even it out. Cook at 180 degrees for 30-40 minutes until the topping is starting to brown.