Grease a roasting tin with a base measurement of 23 x 18 cm (9 x 7 inches), and line the base with nonstick baking paper. Spoon the syrup and sugar into the base. Toss the bananas in the lemon juice, then arrange cut side downwards in the tin.
Heat the butter, sugar and syrup for the gingercake gently in a medium saucepan, stirring until melted. Take the pan off the heat.
Beat the eggs and milk in a jug, then mix the flour, bicarbonate of soda and ginger in a bowl. Gradually stir the milk mixture into the pan of melted butter, then stir in the flour mix and beat until smooth.
Pour the mixture over the bananas, then bake them in a preheated oven, 180°C (350°F), Gas Mark 4, for 30 minutes until well risen and the centre springs back when pressed.
Leave to cool for 5 minutes, then loosen the edge and invert the tin on to a large plate with a rim. Remove the tin and lining paper, then cut the pudding into portions. Serve drizzled with a little extra syrup or custard.