Many households could see their energy bills jump by more than £300 a year as their fixed-rate tariffs come to an end, a price comparison site has warned.
There are nine such deals expiring this month, including popular options from the likes of British Gas, npower and First Utility, at which point customers will be automatically switched to their supplier's standard tariff.
While the average household can expect a hike of around £90, First Utility customers could be particularly hard hit, according to GoCompare.com.
Those on the iSave Fixed V23 August 2015 tariff are facing hikes of up to £318 in the Norweb region, which includes Liverpool and Manchester. Those living in the east can expect a slightly less painful hike of £280, while southerners will be hit with an average £270 increase.
The price you pay for energy is determined not only by your supplier but also where you live, hence the price differences noted above.
While the switch will be bad news for most households, some will actually be better off when their deal expires, because their suppliers' standard tariff is actually cheaper.
These include British Gas Fix & Control Aug 2015, Fix & Reward August 2015 and Sainsbury's Energy Fix & Reward August 2015 customers, who will see their bills drop by an average of £58.06, GoCompare.com noted.
Regardless of whether bills rise or fall, the price comparison site called on all households reverting to a standard tariff to switch once more. Such deals are almost never the cheapest on offer, it said, with households able to save as much as £300 by choosing the cheapest deals instead.
The Energy Saving Trust (EST) has compiled a list of simple steps households can take to reduce their energy usage throughout the year.
:: Switch off standby
Save around £30 a year just by remembering to turn your appliances off standby mode.
:: Do not waste water
Using a bowl to wash up rather than a running tap can save £30 a year in energy bills, according to the EST.
Only filling the kettle with the amount you need will save a further £7, while reducing washing machine use by just one cycle per week will save £5.
:: Spend less time in the shower
Spending one minute less in the shower each day will cut £10 off your energy bills each year, per person. With a water meter this will save a further £15 off annual water and sewerage bills.
:: Turn off lights
An obvious one, but EST says many people are still not in the habit of turning lights off after use. Doing so will save you a further £15 on your annual energy bills.
More detail on the EST's saving tips can be found at http://www.energysavingtrust.org.uk/domestic/energy-saving-quick-wins