Mix together the flour, mixed spice and cinnamon in a large bowl. Add the butter and rub in with your fingertips until the mixture resembles breadcrumbs. Stir in the sugar, currants and glacé cherries.
Whisk together the egg and milk in a separate bowl, add to the fruit mixture and beat thoroughly.
Pour the mixture into a greased 20 cm (8 inch) square cake tin lined with nonstick baking paper. Sprinkle the top with a little demerara sugar, if liked. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 1–1¼ hours until the top is firm but springy to the touch; a skewer inserted into the centre of the cake should come out clean. Leave to stand in the tin for a few minutes, then turn out on to a wire rack to cool completely. Cut into squares to serve.