Competition watchdog the Competition and Markets Authority has launched a review of price comparison websites.

The CMA’s review sets out to investigate public awareness of how they earn their money and the level to which they actually benefit consumers.

The probe will consider concerns such as whether consumers could be made more aware about how the sites earn money and how this affects their service.

It will also examine if arrangements between the sites and their suppliers might restrict competition.

The review – which will take in sites such as Compare the Market, Go Compare and Zoopla Property Group-owned uSwitch – is already arousing controversy.

Talal Fathallah, from energy firm Flipper, said: “Price comparison websites make a huge amount of money from customers through commissions, something which is often unknown by customers.

“This situation is only made worse by the fact these sites are not required to be whole of market and able to favour deals which make them the most money.

“The industry model is broken. It promotes the big players in the market at the expense of the little guys and customers. Customers should come first.”

However, the CMA itself is stressing the positive in re-visiting a subject where it has already said that comparison sites do not need to show the cheapest deals.

Andrea Coscelli, CMA acting chief executive, said: “Digital comparison tools have played a big part in changing markets for the better, bringing new ways of doing things and forcing businesses to up their game.”

“Consumers have benefited as choice and access to goods and services have grown.”

Gillian Guy, chief executive of Citizens Advice, said the methods by which sites select deals should be more transparent, adding: “We welcome the CMA’s study into how people use price comparison websites – which we hope will make things clearer for consumers. Any recommendations from this investigation will need to take into account how consumers behave and make sure people have a process which is clear and easy to use.”

In 2012 YouGov polling on price comparison websites found that just 22pc of the public believed the sites were impartial, with almost a third of people (30pc) unaware that the websites were being paid by providers for a switch.

Consumer minister Margot James said: “Consumers deserve to have access to the best deals and the clear, reliable information they need to make the best decisions.”