A price comparison website is to be investigated by the competition watchdog over its contractual arrangements with insurers that could be resulting in consumers paying more for home insurance.
The unnamed site may be stopping the insurer's products being made available more cheaply on other comparison sites, restricting competition and causing higher prices, the Competition and Markets Authority (CMA) suspects.
It also warned that it will take "enforcement action" against firms that break the law.
In its final report into the use of price comparison sites, the antitrust watchdog's wider findings include setting clear "ground rules" for all online comparison tools.
This includes communicating how they plan to use people's personal data, and clearly displaying important information like price and product description.
The principle recommendations of the CMA's report demands that all sites should be clear about how they make money, how many deals they're displaying and how they are ordering the results.
It should also be made as "easy as possible" for people to make effective comparisons or use different sites, the CMA said.
Andrea Coscelli, CMA chief executive, added: "Our study has found that most people in the UK have used a comparison site at least once, so it is vital that everyone gets the benefits they deserve.
"The good news is that more than 90% of the people we surveyed were very or fairly satisfied with the sites they used.
"But we have also found that improvements are needed to help people get even better deals."