Nigella's recipe for Chocolate Pistachio Fudge uses condensed milk as an ingredient. In Australia, we have both sweetened condensed milk and evaporated milk. Do you mean the former? I used sweetened condensed milk and the recipe was terrific but I don't know if I've unintentionally improvised or used the correct ingredient?
Most countries have both types of canned milk - evaporated and condensed milk. Evaporated milk has about 60% of the water removed but is not sweetened. It is useful in areas without refrigeration as can be stored at room temperature and then mixed with water to use as a substitute for fresh milk (though needs refrigerating after opening). It can be used in sweet and savoury cooking.
Condensed milk does contain sugar (about 45% of the total product) and so is usually used for sweet recipes. The terms sweetened condensed milk and condensed milk are used synonymously for this product. It is this sweetened version that is used in Nigella's Chocolate Pistachio Fudge (from Nigella Express) and also in the One-Step No-Churn Coffee Ice Cream (from Nigellissima).