I've never had to clean the inside of a kettle before so I did some google research and found that cleaning the kettle with half vinegar and half water should do the job. Here's the before, during and after!
Water Quality: For the first few days I didn't notice any taste difference in the water. The kettle did smell a little of vinegar. A few days later I noticed a flavour in the water so I popped a halved lemon in, filled up the kettle and boiled it twice. Now it smells lemony fresh!