Preheat your oven to 190C and place 12 muffin cases in the muffin tin.
Crumble Topping
Mix the flour and sugar together in a bowl.
Cube the unsalted butter whilst chilled and add to the flour and sugar.
Rub the butter with the flour and sugar using your fingers until you have a crumb consistency. Then set aside till later.
Blackberry Sponge Muffins
Add the flour and baking powder to a bowl. Then add in the margarine, sugar and eggs. Beat until it is mixed (an electric mixer will make it quicker but not essential).
Fill each of the muffin cases around half full with the sponge mixture.
To the top of each sponge mix add a handfull of berries. Then push slightly into the mix.
Sprinkle the crumble topping onto each muffin.
Put the muffin tin into the oven and cook for between 25 and 30 minutes until the crumble is golden brown on top.