The "big five" comparison websites are directing callers to energy tariffs that earn them commission despite being asked for the cheapest deal - months after they faced allegations that they used similar tactics online, it has been claimed.
Collective switching website The Big Deal has released recordings of phone calls and transcripts from last month in which it claims that all five of the biggest comparison sites - uSwitch, Go Compare, MoneySuperMarket, Compare the Market and Confused.com - failed to mention deals that did not pay them a commission.
In the case of uSwitch, the difference between what it claimed was the cheapest deal and the actual lowest tariff was £60, The Big Deal said.
Ofgem launched a consultation on the code governing the sector in August, with the newly revised rules announced last month
USwitch said it was taking the allegations "extremely seriously".
A spokeswoman said: "We have very strict guidelines in place for our call centre advisers to follow and these include informing customers of the cheapest deal available, whether we can switch them to it or not.
"We are investigating this matter fully and will take disciplinary action with any individual found to have breached these guidelines."
In October last year The Big Deal alleged that comparison sites were filtering out the tariffs which do not pay commission.
But The Big Deal co-founder Will Hodson said its latest investigation showed the sites were "behaving as badly over the phone as they are online", adding that those likely to be using the call centres were the elderly or those unable to afford access to the internet.
The website said its 'mystery shopper' calls resulted in uSwitch claiming a deal from Scottish Power for gas was the cheapest when there were six lower tariffs, including one that was £62.57 cheaper.
In other calls, uSwitch claimed a tariff from First Utility for dual fuel was the cheapest when The Big Deal found four better deals including one that cost £30.90 less, and Go Compare claimed a Scottish Power tariff for gas was the cheapest when there was another for £18 less.
MoneySuperMarket, Compare the Market and Confused all claimed a deal from Green Star Energy for gas only was the cheapest when there was another tariff that was £11 less expensive, The Big Deal said.
It claimed all the cheaper deals that were not mentioned to callers were from companies that did not pay the websites a commission.
Ofgem launched a consultation on the code governing the sector in August, with the newly revised rules announced last month.
The regulator has banned sites from automatically showing a partial view of tariffs from suppliers paying commission to it.
Instead, they must show all those available in the market unless customers actively choose to see a smaller number of tariffs.
Mr Hodson said: "After being caught out for misleading customers on their websites, you might expect comparison sites to have cleaned up their act.
"Instead we see even dirtier tricks. Telling outright lies to society's most vulnerable is as bad as the dark days of doorstep selling.
"Trust has been broken. Far from being consumer champions, switching sites are letting people down. We deserve answers - honest advice should not be too much to ask."
MoneySuperMarket spokesman Stephen Murray said: "We completely deny the allegation that we lied to the customer. The telephone operator stated at the start that there were products available which she couldn't switch the customer to.
"However, having reviewed this call, in this instance we feel we could have made that clearer. We are reviewing what we say to customers to ensure this is always crystal clear in future."
A spokesman for Compare the Market.com said: " This mystery shopping exercise merely demonstrates that price comparison websites provide a valuable and transparent service to consumers.
"Unfortunately Zog Energy does not allow us to switch customers directly. Customers cannot use our telephone service to switch to Zog Energy - they have to go direct through the supplier's website to do so.
"The shopper was shown the whole of market when he searched for tariffs online. When he then decided to call our customer helpline to switch through an adviser, it was made very clear that his current tariff was being compared to a wide range of tariffs currently available through comparethemarket.com.
"Therefore, all quotes he was given over the phone were tariffs available to him through comparethemarket.com rather than the whole of market.
"This process is clear and easy to use. We refute all claims that we misled the caller or offered an uncompetitive tariff."
