Preheat the oven to 180°C/fan 160°C/gas mark 4. Grease a 1-litre loaf tin and line the base with baking parchment.
Beat the butter and sugar together until light and fluffy. Add the eggs gradually, beating well after each addition. Beat in the golden syrup. Sift in the flour and mixed spice and fold together until just combined. Fold in the mashed bananas and mixed peel.
Spoon the cake batter into the prepared cake tin and bake for 50-60 minutes until a skewer inserted into the centre of the loaf comes out clean. Remove the loaf from the tin and allow to cool on a wire rack for 15 minutes. Cut into slices to serve.