If you've fallen behind on your energy payments, and failed to work with your energy company to find a way to pay off your debt, your electricity may be cut off. Your energy company probably won’t charge you anything if they disconnect your supply. However, you will be charged a reconnection fee, and asked to pay associated costs, when you want to be hooked back up to the grid.
Reconnection fees vary between suppliers so you’ll need to contact your energy company to find out how much you’ll need to pay.