Despite what the name suggests there is no actual cap on energy prices. The cap is based on how much you pay for gas and electricity per unit and standing charges. Therefore if you use more, you will pay more.
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Here is a link to moneysavingexpert. We can see what Martin Lewis has to say…
https://www.moneysavingexpert.com/utilities/what-are-the-price-cap-unit-rates-/