QuantumBrewer knows me well
You don't need an electrician to work on 240V appliances (unless you live in Queensland), but it's highly recommended if you don't have a solid understanding of the wiring rules. Not knowing whether you need to earth the kettle is a pretty clear indication that you don't have a solid understanding of the wiring rules. Another is your mention of two leads, two powerpoints - that doesn't work unless they're on different circuits. A single standard circuit should only deliver 10A, even though it's fused at 16. Either way, it's not enough for your two elements. If the two points are anywhere near each other, they'll be on the same circuit - usually you've got a circuit for each side of your house, or one for the kitchen and one for the rest of the house, etc. Basically, you need a sparky anyway to wire up the house so you've got enough power to your elements, so you might as well get him to wire the HLT as well while he's there. Yes, you need to earth the HLT, and that silicone gasket seems to indicate that the element won't earth it for you.
A possible alternative would be to stick to one element, making it take longer to get up to temp, but saving you having your house rewired. I still highly recommend the sparky for the wiring job, though, because you don't know what you're going to do wrong - exposed conductors, mechanical integrity, IP enclosure, etc.
