Siobhan Parker of Which? stated that the move meant people should review their services.
"Everyone's feeling the post-budget pinch and making sure you're getting the best deal for your home energy is a smart and easy way to take some of the pressure off," she explained.
"If you havent compared your rate with the competition lately, now is the time. We can help you compare prices, switch for free and save money."
Since the start of this year, the other five of the 'Big Six' have gradually introduced price increases for their energy tariffs.
npower was the first to do so, raising its gas and electricity by an average of 12.7 per cent and 17.2 per cent from January 5th.
Click here to run an energy price comparison, and see if you could be paying less for your gas and electricity.