The review of 17 leading aggregator sites followed a warning by the watchdog in May that some sites - which are used by consumers to find the best deals on insurance and other financial products - could be misleading customers by failing to provide accurate information.

The FSA visited a sample of the firms responsible for the 17 Web sites that were assessed during the initial review and found that many of them had made improvements to their Websites and processes. However, the FSA says firms need to provide more clarity about the levels of excesses that apply to policies, and to spell out the assumptions made about applicant requirements when delivering quotes.

The watchdog also probed advertising claims made by the aggregators and found that although the majority were clear and fair, a small number gave consumers a misleading expectation of the firm's market coverage and the amount they could save on insurance premiums.

Dan Waters, the FSA's director of retail policy and conduct risk, says: "It is imperative that all comparison websites provide clear information so that consumers can make informed decisions. We have contacted all websites involved in our review, to set out our findings and the standards we expect. Where needed, we are requiring firms to take prompt action to address our remaining concerns."

The FSA's action was prompted by warnings from the British Insurance Brokers' Association (Biba) that some sites could be breaking the industry's voluntary conduct of business rules.

Last year UK financial policy group the Resolution Foundation called on price comparison Web sites to introduce a voluntary code of practice to ensure transparency in their rankings of competitive financial products.

The FSA's consumer website - Moneymadeclear - provides help for consumers on purchasing insurance through comparison websites.