Lucy Hunter, Sainsbury's Car Insurance Manager said: "Premiums have been rising steadily and it has been predicted that this year they could increase by as much as 10%.
"However, by shopping around, you can still reduce your premiums significantly. Unfortunately, many motorists aren't prepared to do this.
"Our research shows that one in five motorists only obtained one quote the last time they bought car insurance and of those motorists who didn't obtain more quotes, 19% said it was because they couldn't be bothered or didn't have enough time."
Gender continues to have an impact on how much you pay for your car insurance, with the average premium for men being £518.46 as opposed to £442.28 for women. Indeed, between July 2006 and July 2007, the average car insurance premium for men increased 5.2% as opposed to 3.1% for women.
Age also has a huge influence on the premiums you pay. Unsurprisingly, as they are responsible for the highest frequency of car insurance claims, motorists under 25 have seen the biggest increase in their car insurance premiums, rising by 6.4% since December last year, and 11.2% since July 2006.
In contrast to this, motorists aged over 65 saw the cost of their car insurance only increase by 0.79% and 2.7% respectively, the lowest rise for any age group.