More than three-quarters of adverts for financial products are misleading, with many failing to warn consumers of the risks involved.
Accountants Grant Thornton said 76 per cent of the adverts and promotions which it inspected failed to meet the standards required by City watchdog the Financial Services Authority.
It said some were "wildly misleading".
Problems uncovered by the group included rates being advertised that were not available, the use of scare tactics, making wide-reaching claims that were not true, and excessive use of small print.
It called on companies to play by the advertising rules and not to exploit consumers' ignorance about financial products.
Grant Thornton's Financial Markets Group reviewed 117 financial promotions, including newspaper adverts, websites and other literature which appeared in late 2005 from 94 companies.
It found that headline-grabbing rates used in promotions were often not available in practice. Firms would also claim that their premiums were cheaper than those of their competitors by comparing a basic product with one that offered more cover.
Companies often used scare tactics, such as warning that one in three people would get cancer during their lifetime, while failing to point out that some forms of cancer were not covered by the product being advertised.
They ignored the need to include risk warnings required by the FSA, such as telling people that the value of their fund could go down as well as up.
Other problems included making wide-reaching claims that were not true or could not be proved, such as saying the product offered the best rates.
The survey also found a wide range of jargon which would confuse consumers and an excessive use of small print.
Overall, the group found significant flaws in 84 per cent of adverts for investments, 81 per cent of mortgage promotions and 61 per cent of insurance adverts. The FSA requires all financial adverts to be clear and fair. They should not be misleading.
The group found that 65 per cent of mortgage promotions and 58 per cent of those for investments needed to improve the clarity of the product or service being offered, while 76, per cent of adverts for investments failed to warn consumers of the associated risks.