Hi Tony, The electricity comes from the mainland via undersea cable.
Ian, I didn't use the wrong law. Ohms law still applies.
V=IR Therefore if the voltage goes down the current also goes down. If the voltage goes down 10% then the current also goes down 10%.
Then the other law applies P=VI but as both the current and the voltage have gone down the power is 90% of 90% (81%) and therefore your kettle which was a 3 KW at 240 volt would become a 2.43 KW kettle at 216 volts.
If you read the little label on most appliances you will see they give the wattage as a max. wattage which of course may go down with the voltage.
This of course is only true with regard to kettles which only have resistance and not to electric motors, transformers etc which have inductance and so you would use impedance instead of resistance and at this point ohms law goes out of the window and Mr Henry comes into play.
Sorry if I am boring everyone.