Heat the oven to 160C/fan 140C/gas 3. To make the parkin, sift the flour, ground ginger and mixed spice into a large bowl, add the oats, and mix. Melt the golden syrup, treacle, sugar and butter in a saucepan, until the butter has melted and the sugar has dissolved. Pour the hot mixture into the dry ingredients and mix well.
Add the egg and milk, then mix again briefly. Pour the mixture into a buttered and lined 900g loaf tin. Cook for 45mins-1 hour, or until a skewer comes out clean. The cake will be sticky and dense but keep checking every 5-10 minutes after 45 minutes with a skewer until cooked. Cool in the tin.