Analysis by MoneySuperMarket shows 19 tariffs end in June, 17 in July and a further 18 in August from the likes of EDF, British Gas, Scottish Power, Npower and smaller suppliers such as GnERGY and Affect Energy.

When these deals end, providers will roll customers onto their Standard Variable Tariff (SVT), which is typically their most expensive. Households on these deals could see their bills rise by £192 on average if they don’t take action and secure another fixed rate before their tariff end date.

The comparison site said average bills are higher now than 12 months ago, but there are still deals to be found.

For example, its deal with Co-operative Energy offers a one-year fixed tariff to new Co-op customers only, with annual bills starting from £849.47.

Stephen Murray, energy expert at MoneySuperMarket, said, “Even though the price of average fixed rate tariffs has jumped significantly in the last 12 months, switching to one still means customers can significantly minimise the increase they will see by rolling over onto a standard variable tariff.

“It’s still a competitive market out there, whether you want to go with a Big Six or smaller supplier – households just need to make sure they are on the best possible deal and not paying £200 too much for their energy.”

The majority of fixed deals come with exit penalties designed to deter customers from switching during the period.

However, these cannot be charged within 45 days of the tariff end-date, meaning customers have over six weeks to switch, penalty-free.