(ShareCast News) - An investigation into energy price comparison websites will be shifted to the Competition & Markets Authority (CMA) from sector regulator Ofgem.It was confirmed on Wednesday that Moneysupermarket is not involved in the investigation, while Zoopla's uSwitch said it was working with the competition watchdog.Price comparison websites are suspected of rigging the market by agreeing not to compete with each other for certain Google search terms when consumers search for the best deals.The CMA said it was "investigating a suspected breach of competition law by some price comparison websites that offer energy tariff comparisons in relation to paid online search advertising," though did not name the parties it is investigating.In a statement, uSwitch said: "We have supported Ofgem with information in relation to this matter and will provide the CMA with any further information, if asked. This case is currently at an information gathering phase as the Ofgem decision notice specifies. We have no further detail on the nature of the case."The Guardian suggested on Tuesday that the actions of Ofgem staff ahead of the investigation had meant the probe needed to be moved to an alternative body.Ofgem found its staff had, before the formal investigation begun, contacted the websites to encourage them to change their behaviour when it came to buying advertising on search engines such as Google, the newspaper said. Once the investigation began, Ofgem realised its earlier activities could call into question the regulator's own impartiality.The CMA will investigate and is scheduled to report in August.Broker Peel Hunt said it had verified from Moneysupermarket that is was not involved in this investigation.