In order to remove limescale deposits from around the lid of your kettle we would recommend a solution of one part white vinegar and two parts water.
You may need to soak a kitchen towel in the solution and leave on the marks if they have been left for a long time.
Only use a nonabrasive cloth to remove, such as a microfibre cloth.
We would not recommend most proprietary descalers as these can often damage the paint on enamelled kettles.
To avoid a build-up, particularly in hard water areas, do this monthly after you have descaled your kettle.