Put the water and sugar in a saucepan and heat gently, stirring, until the sugar has dissolved. Stir in the butter, cocoa powder, bicarbonate of soda and instant coffee and bring to the boil. Simmer for 5 minutes, remove from the heat and set aside to cool.
Beat the flour and eggs into the cooled coffee and chocolate mixture until smooth. Divide the mixture evenly among foil cake cases arranged in a 12-hole deep muffin tin. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes until risen and firm. Transfer to a wire rack to cool.
Make the icing. Put the chocolate, butter and syrup in a heatproof bowl set over a saucepan of gently simmering water, stirring until melted. Remove from the heat and leave to cool to room temperature, then chill until thickened. Spread over the cupcakes, top with a chocolate coffee bean and leave to set.