Customers who don’t switch will be automatically moved onto standard variable tariffs, which are typically more expensive in comparison to fixed deals.

According to analysis by energy comparison site Energyhelpline.com, 12 suppliers have tariffs ending at the end of August, including four of the big six – British Gas, EDF, npower, and ScottishPower.

The additional cost of big six tariffs ending average at a £193.16, which is £35.32 more than the average hike across all suppliers.

Victoria Arrington of Energyhelpline.com said: “With wholesale costs continuing to rise, fixed tariffs often offer better value for most customers.

“A fixed deal could lock in lower energy prices for up to 36 months. This means you’ll dodge those less predictable cost increases which can happen on a variable tariff.”

If your tariff has less than 49 days left, you can switch without having to pay a penalty fee.

For more, read YourMoney.com’s guide to switching energy supplier