Bad example!
You might think all that limestone in Derbyshire will mean the water in Derby is pretty "hard", but most water round there comes from the Ladybower/Derwent reservoir complex, all acid moorland runoff, and very "soft"! (Any scum in the kettle comes from what the water company adds to stop the water rotting the pipes).
I might have Welsh roots and live in Wales, but I was brought up near (6 miles from) Derby. All my early brewing had "a bit of gypsum" added to my brewing water.
And for the rest of the UK: The paranoia exampled in the OP is born of American brewing scribblings, and their seeming fear of anything that might be in the water. Most British tap water is fine for brewing (with perhaps some basic treatment here and there). We're only a little island, the water doesn't get chance to dissolve much into it (perhaps some exceptions where water is sourced from deep bore holes?).