Preheat the oven to 180C/350F/Gas 4. Grease and line a loaf tin.
Put the flour and butter into bowl and rub together until the mixture resembles breadcrumbs. Stir in the caster sugar and mixed spice.
Mix the marmalade, orange juice, raisins and one tablespoon of milk together in a separate bowl.
Stir the marmalade mixture into the flour mixture, then spoon into the loaf tin. Sprinkle over the demerara sugar.
Bake for 30-35 minutes, or until risen and golden-brown and a cake tester inserted into the middle comes out clean.