Over 140,000 households could see their energy bills climb by as much as £190 at the end of January, with 47 fixed price deals set to come to an end.
The average cost for households which do not switch will be £114, according to data from uSwitch.com.
In total, such price hikes will cost a cumulative £16m, with deals from 13 suppliers scheduled to finish in the coming weeks.
Customers who don’t move to a cheaper deal will typically be rolled onto their supplier’s default, or ‘Standard Variable’ tariff, which are among the worst value energy plans on the market.
Those supplied by EDF, Shell Energy and Scottish Power will see even greater hikes of £192, £175, and £146 respectively.
The change in tariffs comes at a notoriously tricky time for UK households, with Yougov data showing that half of those already in debt find themselves in an even worse financial position following Christmas, with 20 per cent worried they will be unable to recover.
Ofgem is expected to announce a decrease in its energy price cap at the beginning of February, but the lower rate won’t come into effect until 1 April.
Cordelia Samson, energy expert at uSwitch.com, says: “People are already feeling the strain on their wallets after Christmas, and the last thing they need is for their energy bill to shoot up.
“Anyone whose fixed energy deal is coming to an end soon will be rolled on to an expensive Standard Variable Tariff if they don’t choose a new, cheaper plan. So now is the time to take action.
“In the past six months we’ve seen the lowest-priced deals becoming even cheaper. Households can take advantage of more than 50 fixed deals available for less than £1000 per year and switch now.