Line a 20 cm loose bottomed cake tin with non stick baking parchment. Preheat the oven to 180 C, 350 Fan Gas 4.
Sift the flour with the cinnamon or mixed spice and salt. Rub in the butter until the mixture resembles fine breadcrumbs. Stir in the sugar, blueberries and apples. Add the eggs and mix evenly.
Spoon into the prepared cake tin and bake for 1 1/2 to 2 hours. Test by plunging a skewer into the centre of the cake tin- if it comes out dry the cake is ready. If not, cook for a little longer.
Turn out of the tin and leave to cool on a wire rack.