Scores of energy customers facing exorbitant bills will not be entitled to a cut under the new energy price cap, a consumer group has warned.

According to Which?, just under a third of dual-fuel deals will not be capped - leaving customers hundreds of pounds out of pocket.

The cap, which is set to be introduced by the end of this year, will only apply to default tariffs (usually variable), so those on expensive fixed tariffs will not benefit from it.

Which? claims to have identified more than 70 fixed deals more expensive than the proposed average cap of £1,136 a year, with customers paying up to £200 more.

Ofgem claims that the millions of households that will benefit will save an average of £75 a year, however energy experts have warned that consumers could still save more by comparing and switching supplier.

Alex Neill, Which? Managing Director of Home Products and Services, said: “While this cap may cut energy bills for some, people shouldn’t be lulled into a false sense of security that they are getting the best deal.

“As our research shows, the cap won’t cut everyone’s bills and you can save more by switching.”

The price cap will vary between regions, depending on how much it costs to provide gas and electricity to a particular area, and the actual amount you pay will still depend on usage.

The cap will be set at £1,124 in Southern Scotland, £12 lower than the UK average, and £1,154 in Northern Scotland, £18 higher than the UK average.

Of the Big Six suppliers, Ofgem figures show that Scottish Power customers could save the most under the cap, with medium energy users seeing their bills cut by an average of up to £121 a year.

However, Which? has identified almost 100 energy tariffs which already cost less than the proposed cap, with the cheapest deal costing £258 a year less for a medium energy user.

This means customers could save more than three times as much by switching, rather than relying on the cap.

Mr Neill added: “The price cap is only a temporary fix, what is now needed is real reform to create competition, promote innovation and improve customer service.

“If you are unhappy with your current energy provider, you should look to switch now to another supplier and potentially save almost £400 a year.”

Martin Lewis, founder of consumer site Money Saving Expert, has also warned that energy companies are likely to set their tariffs to within £1 of the cap.

While he praised Ofgem for setting the cap lower than expected, he said: “The savings are still pitiful compared to the amount people would get if they switched and went to the market’s cheapest providers.

“There is a real concern the imposition of a cap will give people a false sense of security that doing nothing is fine.”