Fourteen price comparison websites are to be investigated following concerns that some of them could be misleading customers.
The Financial Conduct Authority (FCA) is looking into potential conflicts of interest, examining whether any sites are promoting deals they want them to buy and focusing too much on price rather than customer service.
They will also look into cases where comparison sites are owned by insurers themselves.
FCA spokesman David Cross said: "If insurers happen to own a particular price comparison website there is a concern that could create a conflict of interest whereby their products are promoted over others.
"When someone searches for something; are they necessarily getting the best deal for them, or are they just getting the deal the website want to give them?"
The review will question company heads about whether the customer or profit is really at the heart of a business model and examine the "expectation gap" for customers who may money on insurance premiums only to face problems when claiming on their policy.
Mr Cross said: "Price isn't necessarily the best marker of an insurance deal. When you come to claim, if you find out that you can't, then obviously that money's been spent for nothing."
The FCA stressed that comparison sites "perform a valuable service for millions of people" and said almost half of all internet users had used them to research motor insurance, with four in five going on to buy it through the same site.
