Diamonds are supposed to be a girl's best friend, but when it comes to car insurance for women drivers all that glisters is not gold.

Phone up Diamond, the insurer that makes great claims of offering women cheaper rates and you would think you had walked into a branch of Asprey & Garrard for the prices charged.

Diamond is part of the Admiral insurance group and reputedly offers women better deals, especially those living in the south east and Scotland.

A spokesman said: "Women have better claims records than men and far less motoring convictions. It's because of that they are a lower risk and you can give them cheaper insurance."

But research carried out by Jobs & Money shows that for a female driver, aged 25 and living in central London, Diamond quoted almost double (£600.60) the lowest price. The best quote comes from Churchill at £313.95. The worst came from Liverpool Victoria at £633.15.

For female drivers aged 25, this time living in Manchester, Diamond come out bottom at £773.85. Churchill come out top at £300.30 for the year.

Diamond's spokesperson was at a loss to explain the vast difference in price. He said: "The reason the quotes are higher is because they are based on a fictious person who's not registered on the electoral role, and we can't do a credit check on them - so the prices are loaded."

But when we pointed out that all the other insurance companies quotes were based on the same criteria, he commented: "We do keep an eye on the market. We don't liked to be priced out of the market. We'll be looking into this."

The principle that women are cheaper to insure is well established. With survey after survey showing women are better drivers than men, insurance companies quote them lower rates than their male counterparts.

Statistically, women have lower fatality rates than men travelling over the same distance. They drive smaller cars and don't feel the need to impress other drivers or passengers with Michael Schumacher-style driving, says the AA.

Unlike men, women spend less time on motorways and more time in urban areas. And the types of accidents they are involved in are minor in comparison.

Men, on the other hand, have accidents at high speeds and in big cars, according to Andrew Howard, head of road safety for the AA motoring trust.

"When you look at the stats men have more over-taking accidents which derive from thrill seeking, competitive behaviour than women. Men want to do expressive things with their cars. Whereas women see their car as something to get them from A to B, rather than something to show off in," he says.

A spokesman from the AA said: "Women are consistently seen as better risks on the roads than men, until they reach 55."

Women also have better claims histories than men and cost insurance companies less. The average claim for a man is £1,916 where as the average cost of a claim from a women is £1,546, says research from Diamond.

Diamond is not the only firm that falls down in our insurance test drive. Auto Direct, another insurer with flambouyant marketing, claims on its website to offer the "lowest car insurance rates for women or your money back".

But it is no where near the top in our research. Its quote for a 25-year-old driver in Manchester is £507.51. This is £207.21 dearer than the cheapest at £300.30. Its spokesman said: "We're a broker and therefore direct insurers can offer better rates."

Women on Wheels, a marketed product for women from Endsleigh intermediary insurers, does deliver the goods. Insuring the 35-year old driver, it comes out top in both London and Manchester at £264.58.

Norwich Union, however, offered the highest premium for London drivers at just under double the price of £516.96.

Once again, Diamond have poor best buy rates in Manchester, offering a 35 year old driver £685.35 for the year, almost two thirds of the price of Women on Wheels.

A spokesman for Endsleigh said: "We dropped all our rates by roughly 10% at the end of last year to make us more competitive across the board. We are also very competitive for teachers and professionals like doctors, nurses and solicitors."

So if you weren't a professional you may have faced even higher rates.

Finally, the overriding message here for women drivers is to shop around for your insurance and don't be fooled by marketing gimmicks.