Descaling a kettle

I’ve just read the thread on mumsnet recommending all sorts of commercial methods for descaling, I thought we all knew that a lemon is the answer. Even if you’ve juiced the lemon, cut it into quarters, put it in the kettle with a pint or so of water, bring to the boil and leave it to do its thing. Rinse and away you go. Cheap, easy, no chemicals, dah de dah.