[Tatsfield]

The area in which the sat nav will work is governed by the decision of the developers as to what areas they include on the disc. There is no reason why some areas should be on one disc and others on another apart from the capacity of the system to read the data on the disc. I used to have a car with a disc operated sat nav and it was possible, while they were available, to buy various discs at differing prices of maps of parts of Europe, maps of all of western Europe and maps of eastern Europe. I don't know what areas and what groupings the sat nav designers made but you could try shopping around on the internet for second hand discs to see what areas are available.