Preheat the oven to 190°C and grease a 20cm square cake tin.
Cream butter and sugar, then beat in eggs and fold in flour and milk.
Level the batter in the tin and bake for 35 to 40 minutes until golden-brown.
Cool the cake for 5 minutes before turning out onto a wire rack to cool completely.
Dissolve sugar in water over heat and stir in lemon essence for the syrup.
Beat filling butter and icing sugar together until fluffy.
Remove the cake crust and slice the cake in half horizontally.
Brush the bottom layer with syrup, spread with buttercream and jam, then sandwich with the top.
Wrap in cling film and chill for 2 to 3 hours.
Top with apricot jam and rolled marzipan, then cut into 4cm squares.
Mix fondant icing sugar with hot water and reserve small portions for coloring.
Coat each cake square with white icing and let set on a rack.
Mix blue and red food coloring into the reserved icing portions.
Pipe Union Jack patterns onto the cakes and place them in paper cases.