Stir the milk and vinegar together in a jug. Allow to sit for at least 15 minutes.
Preheat the oven to 180°C (160°C fan) / 350°F / Gas Mark 4.
Prepare the cake tin by greasing with margarine and lining with baking paper.
Sift the flour and baking powder into a mixing bowl.
Add the margarine in little blobs to the bowl.
Using your finger tips rub in the margarine into the flour until it resembles breadcrumbs.
Next, stir through the sugar, dried fruit mix and mixed fruit peel.
Stir the golden syrup through the sour milk you prepared earlier.
Pour the milk mixture into the dry ingredients, and stir with a mixing spoon until just combined.
Scoop the mixture into the prepared cake tin and level out the surface.
Bake on the middle shelf of the oven for 1 to 1½ hours. The cake is ready when it feels firm to the touch, is golden on top, and the sides have started to pull away from the tin. A skewer inserted into the centre should come out clean.
Cool the cake in the loaf pan for 20 minutes before carefully removing from the pan and setting on a cooling rack to cool completely.
