Customers who fail to switch to a better deal could see bills go up by almost eight per cent. ScottishPower’s Online Fixed Price Energy December 2014 customers have the most at stake, as defaulting to the ‘Big Six’ provider’s standard tariff could see bills increase by £144.93 per year.

Jeremy Cryer, energy spokesperson at Gocompare.com, said: “It can take as much as six to eight weeks to switch to a new supplier, which could leave many consumers languishing on pricey standard tariffs well into the New Year if they don’t start looking for a better deal immediately. There are lots of good deals to be had right now, and they are certainly a far better option than any supplier’s standard tariff. In fact, there are nine sub-£1,000 a year dual fuel tariffs available at the moment.

“If you are reluctant to switch to another fixed deal in case a better one comes along in a few weeks’ time, bear in mind that some suppliers don’t charge an early exit fee, while others charge very little. As such, signing up with these providers is less risky should you wish to switch away again part-way through your contract. That said, others charge as much as £30 per fuel for early exits, so any savings have to be quite substantial to justify taking a hit of up to £60 to leave before the end date.”

See the chart below to find out if your tariff is expiring at the end of the month.