The Telegraph previously revealed that some firms had been offering fixed deals of more than £3,000 per year.
By contrast, the cap is only updated every six months, meaning it has lagged behind the market price rises.
This has kept the price of standard variable tariffs – capped at £1,277 for a typical household currently – artificially low and protected families from the price rises for the moment.
However, analysts expect bills to increase by more than 50pc when the price cap is updated in April.
Martin Young, an energy analyst at Investec, has predicted the limit could increase to as much as £2,000 – a more than £700 increase on the current limit – although he has more recently revised that estimate to £1,900.