I agree that the map seems to show quite large areas of softer water, notably Scotland, Northern Ireland and most of Wales, but when you take population density there are not , in the grand scheme of things, that many people in Scotland etc compared to the harder water areas, ie the South East, Midlands, South, Anglia etc
However, any levels of calcium will scale up appliances, some areas taking longer than others.
The main point of my post was the warning about using non approved descaling chemicals and warranty conditions imposed by appliance makers.