In a saucepan combine the water, caster sugar, brown sugar, vanilla extract, raisins and butter; bring to the boil over medium heat, stirring occasionally. When the mixture boils, remove from the heat and allow to come to room temperature.
Preheat the oven to 170 C / Gas 3. Grease a 12 hole muffin tin or line with muffin paper cases.
In a large bowl mix together flour, bicarbonate of soda, salt and spices. Pour in raisin mixture and carefully stir with a spatula. Fold in the chopped walnuts. Spoon the mixture into the paper cases about 2/3 full.
Bake in preheated oven for 18 to 20 minutes, or until a skewer inserted in the centre of a muffin comes out clean. Remove from the oven and allow to cool before enjoying.