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Over 500,000 energy users could see energy prices rocket by 50% in the summer simply by allowing their fixed-price tariffs to roll over, comparison and switching service uSwitch has warned.

The consumer website said on Thursday (20 July) that 50 fixed energy plans are coming to an end this summer, with 14 fixed-price tariffs from eight different suppliers ending in July alone. Customers on plans that will come to an end this month face an average increase of £274 ($355.9) if they allow their tariffs to rollover.

Npower users could see their bill jump by as much as £399, while those on First Utility and EDF Energy face hikes of £364 and £360 respectively.

While fixed-price tariffs protect customers against sudden increases in price, they can often carry hefty cancellation charges for consumers wishing to switch to a different provider.

According to energy regulator Ofgem, approximately 66% of UK households are on standard variable deals, which are more expensive than the fixed-price option but do not have cancellation charges.

Last year, around 16% of gas and electricity customers switched tariffs, the highest percentage since 2010, and 47% of those who switched moved to small or medium suppliers.

"Switching tariff is incredibly easy and is definitely worth 10 minutes online, on the phone or on an app," said Claire Osborne, from

"You can switch without incurring any exit fees 42 days before the contract end date, and comparing and switching takes just minutes to do."