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Retailers also apply a daily supply charge, irrespective of your level of energy use, and there may also be a discount applied to the bill. Some retailers won't honour discounts on their last bill if you switch away from them before the end of the contract period Many retailers will offer you an extra discount for doing this, but it pays to check if their underlying rates are actually competitive. Retailers claim it's necessary because their costs can go up during the duration of the contract, and so far regulators have sided with the retailers on the premise that ending unilateral variation would lead to higher prices for consumers. [Extracted from the article]