The financial watchdog's survey found that differences in the comprehensive motor premiums quoted by eight insurers for eight hypothetical consumers across a range of ages, professions, cars and licence types, varied from €303 to €5,110.
Calling on insurers to reduce premiums, the Tánaiste, Ms Harney, said the survey underlined the importance of shopping around.
The Labour Party spokesman on Enterprise, Trade and Employment, Mr Brendan Howlin, said it was not acceptable that the cost of cover could vary by up to 500 per cent when most insurers are making substantial profits.
"Neither is it good enough to simply advise people to 'shop around', when many are simply not in a position to do so, due to their work situation or geographical location," Mr Howlin said.
Fine Gael spokesman Mr Phil Hogan said the survey proved that insurers were not passing along to consumers the benefits of lower claim and litigation costs, as well as savings in respect of road safety.
"Young drivers and small businesses in particular require a better response from insurance companies," Mr Hogan said.
Ms Mary O'Dea, consumer director of IFSRA, said publication of the motor survey and a comparative table on current account charges demonstrated the benefits of shopping around.
The average price difference between the cheapest and most expensive companies for the comprehensive motor insurance categories shown was €2,224.
Four companies refused to provide cover to a 21-year-old male living in Dublin with a new provisional licence, with three companies failing to quote female customers in this category.
Motorists aged 22 with a one-year provisional licence will also be refused by some companies.
Ms O'Dea said IFSRA could not force insurers to operate in a particular market.
The tables will help consumers assess the various insurance features available, Ms O'Dea said, and some may opt to pay higher premiums in order to secure the type of cover they want.
However, motor insurance, which is compulsory by law, is primarily cost-driven, she added, with drivers less interested in the level of service on their claims.
The recently introduced obligation on insurers to give customers 15 days' notice of their renewal date will also make it easier for motorists to shop around for cheaper insurance.
The regulator's motor insurance survey will be updated every three months and the table on current account charges will be reviewed every six months.
The surveys, lists of questions to ask and consumer "dos and don'ts" on a range of financial products are available online at www.ifsra.ie.
Surveys on credit cards, home insurance and overdrafts will be published during 2004.
There have been over 4,000 calls to IFSRA's consumer helpline - 1890 777 777 - since May, with the cost of motor insurance the most frequently occurring topic.
