The gap between the standard tariffs offered by the Big Six and the cheapest one has widened “significantly”.

The difference between the average Big Six standard dual fuel tariffs and the cheapest equivalent on the market has increased from £182 to £329 since 2014, according to research by Which?

The Competition and Markets Authority (CMA) previously revealed householders could have been paying around £1.7 billion a year more than they would in a competitive market.

Which? stated it remains concerned the remedies proposed by the CMA will not lead to improved outcomes for consumers.

It is calling on the watchdog to outline how it will evaluate the success of its proposals, including how suppliers deliver better outcomes for vulnerable customers, in its final report, which is expected to be published this month.

Alex Neill, Which? Director of Policy and Campaign said: “It is right that the energy market has been investigated but during this time prices have continued to soar. If consumer trust is to be restored in this market then the CMA proposals must bring about real change in the energy market to benefit consumers who have been paying over the odds for gas and electricity.”

According to Energy UK, prices are not rising as suppliers are “consistently reducing” them on both fixed and variable tariffs.

Lawrence Slade, CEO of Energy UK said: “Deals now start at £734, which is more than £200 cheaper than two years ago, with 53 deals under £900 being offered by over 40 suppliers operating in the market.

“People should take advantage of the fantastic deals out there. Suppliers have made it even easier for customers to switch to benefit from the best offers. This week saw the launch of Energy Switch Guarantee, which companies are signing up to, giving consumers even more confidence to switch provider without any hiccups.”