What is the best method for removing limescale from modern kettles?

Denture cleaning tablets such as Steredent. Depending how bad the limescale is put 1/2 to 1 tablet in the kettle after it has boiled, leave until cool and you will be amazed at the result. Also as it is used for dentures you know it is perfectly safe to use in your kettle as no risk of any deposits left and upsetting your system. There are also specific cleaning products for removing limescale like Calagon but I have a home abroad where the water is extremely hard and cal builds up and believe me Steredent Denture Tablets are the one thing that works every time.