Preheat the oven to 180ºC/350ºF/gas 4. Line a 12-hole cupcake tray with paper cases.
Sieve the flour, baking powder, bicarbonate of soda, ground ginger, cinnamon and salt into a large bowl.
In another bowl, whisk the oil, golden syrup, yoghurt and milk together until well combined. Finely chop and add the stem ginger, along with 1 tablespoon of syrup from the jar. Fold in the flour mixture until smooth and combined.
Divide the cake mixture between the paper cases, then place in the hot oven for 15 to 20 minutes, or until golden and an inserted skewer comes out clean. Leave to cool for a few minutes, then transfer to a wire rack to cool completely.
Meanwhile, make the icing. Sieve the icing sugar into a large bowl, add the margarine, then beat until pale and fluffy. Add the cream cheese and whisk well until smooth and combined. Decorate the cooled cupcakes with the icing, dust with a little ground ginger, then tuck in.