Preheat the oven to 190ºC/375ºF/Gas Mark 5. Put the lemon zest and juice in a saucepan with 2 tbsps of the golden syrup, sugar, butter and 125ml of water. Bring to a simmer and then remove from the heat, and leave to cool slightly.
Mix together the flour, suet, salt and about 150ml cold water to form a soft pliable dough. Roll out on a surface lightly dusted with flour to about 25cm square, 5mm thick. Drizzle the remaining 4 tbsps of syrup over the top and scatter over the apples, leaving a 1cm border of suet pastry around the edges.
Roll into a cylinder shape and using a sharp knife, cut into 2.5-3cm slices. Lay in a baking dish, overlapping slightly. Pour the lemon syrup mixture over the top and place in the oven for 35-40 minutes until the pudding is nicely golden and bubbling. Dust the cooked pudding with icing sugar and serve hot with custard, ice-cream or cream.