In two weeks’ time eight fixed energy deals will come to an end, bringing in an average annual bill increase of 11 per cent - or £108 - for anyone who hasn’t switched to a better deal, reckons GoCompare.
Suppliers with tariffs ending on 30 September are EDF Energy, First Utility, Scottish Power, M&S Energy, and iSupplyEnergy.
First Utility customers in north-west England, who are currently on the iSave Fixed v7 September 2014 dual fuel tariff, will see the biggest average bill increase of all, at £237.65, or 21.9 per cent.
However some First Utility households in northern Scotland could actually be in for a price reduction of £6.57 if they switch to the firm’s iSave Everyday standard tariff when their fixed deal ends.
However, this doesn't mean that it's a good idea for those customers to simply accept First Utility's standard tariff, as they may be able to save even more by shopping around and switching.
The biggest increase for a Big Six customer will be felt by those living in south-east England who are on Scottish Power's Online Energy Saver 23 tariff, with an average price hike of £164.93.
Jeremy Cryer of GoCompare said: "Many households could find that their annual energy bills are set to increase if they don't take action and look for a better deal.”
Energy watchdog Ofgem has forced energy firms to make it easier for people to switch, including a rule that, once you receive notification from your supplier of your fixed tariff coming to an end - usually 42 to 49 days before it's due to expire - you can switch without any exit fees being applied.
“That's exactly when you should start shopping around, as it can take as much as four to six weeks to transfer to your new supplier,” said Mr Cryer.
"Not taking action and just rolling onto your supplier's standard tariff is the very worst option, and even if you think that you will be saving money by doing so, it's likely to be a tiny amount and unlikely to be anywhere near as much as you could save if you compared lots of different tariffs from multiple energy companies.”