Grease a 12 cup muffin tin.
Sift the gluten free plain white flour, baking powder, xanthan gum and salt into a large mixing bowl and stir in the sugar.
Place the eggs, milk, margarine and vanilla essence in a separate bowl and whisk together well.
Fold the egg mixture into the dry ingredients with a metal spoon, then gently stir in the blueberries.
Spoon the mixture into the muffin cups, filling them to just below the top.
Place the muffin tin on the top shelf of the oven and bake for 20-25 minutes, until the muffins are well risen and lightly browned.
Leave the muffins in the tin for about 5 minutes, then turn them out on to a wire rack to cool.