Theresa May’s party has pledged to limit the amount energy giants can charge customers for their electricity and gas bills, ahead of the General Election.
But experts warn this could mean some of the cheapest deals are pushed out of the market, if competition among suppliers is killed off.
Analysis shows millions of homes are on some of the most expensive deals on the market.
These households could save £300 on average by changing to a better deal, according to Moneysupermarket.com.
Instead of a cap, the Government should make it easier to switch and raise awareness of the savings to be had by moving energy supplier.
Stephen Murray, energy expert at MoneySuperMarket, said: “This is not a Big Six issue as many believe.
“A growing number of emerging and challenger suppliers have significant price differentials across their tariff portfolio and a cap would simply push many cheaper tariffs out of the market, resulting in higher prices.
“The energy market is working better than many people give it credit for.
“There is more choice for consumers, more innovation by suppliers and an effective switching industry with 50 suppliers to choose from and huge savings to be made.”
Mr Murray added: “A price cap, whether relative or actual, will lead to many of the best deals disappearing, prices finding a higher level and a growing market of disengaged customers.
“Instead of bringing in a price cap, the Government should spend some money raising awareness of switching and leave the mechanics of an increasingly vibrant and competitive market well alone.”