Put the rice in a large pan with 500ml water and the lemon and orange zest. Bring to the boil, cover, lower the heat, then cook for about 15 mins until all the water has been absorbed. Uncover, stir in the milk and sugar, then simmer for 20-25 mins, stirring often, until the rice is tender and sauce thickened. Cool, then leave at room temperature.
Put the raisins into a small pan with the cinnamon, muscovado and 100ml water. Gently heat until the sugar has melted, then bubble for a min until syrupy. Stir in the cream, then cool in the pan.
Dish up at the last minute - stir a little milk through the rice mixture if it has become 'solid' after sitting for a while. To serve, divide the rice pudding between 8 glasses or small bowls and top with a spoonful of the syrupy raisins.