Britain's biggest price comparison sites are 'hiding' the best energy deals from consumers in order to benefit themselves, according to a consumer group.

The Big Deal website - a business dedicated to finding mass consumers the best energy deal – says that five of Britain's biggest price comparison sites are acting deceitfully.

It alleges that uSwitch, the largest switching site, never showed the cheapest deal over the Big Deal's 13 week investigation, adding that it also regularly hid three of the top five cheapest deals.

One of the biggest problems for customers using price comparison sites is that they use mechanisms to "hide deals where they ask users if they want to see deals they can switch to 'today' or 'now'", according to a statement from The Big Deal.

It says that clicking 'yes' to this option on the websites removes deals which do not earn the price comparison sites a commission from the energy companies, which are often the cheapest deals. The Big Deal says that Money Supermarket and Confused automatically tick the 'yes' option.

It also adds that Compare the Market and Go Compare automatically show users these results without asking the user, adding that "you have to go through several screens to 'filter your results' to see the cheapest deals."

Overall, the report claims, price comparison sites hid around a third of deals via this method, which it claims is breaching EU and UK law.

"Price comparison sites are worth hundreds of millions of pounds, make huge profits and with over 5 million people switching a year are a major part of the energy market," said The Big Deal co-founders Henry de Zoete and Will Hodson in an open letter to the major price comparison sites.

"Yet there is no transparency to how they make their money or how much they charge. Polling by Populus found that 43% of people did not even realise that the sites charge energy companies a commission."

uSwitch hit back at The Big Deal by releasing a statement that says: "We are fully accredited under the Ofgem Confidence Code, meaning that our results tables are always ordered by the savings a customer can make in a fair, independent and unbiased way.

"We are fully supportive of Ofgem's decision to strengthen the code to ensure that all price comparison websites operate to the same high standard."