When buying a new car, some 7.7 million motorists fail to review their car insurance policies, causing them to pay up to £428 million too much every year.
Nearly a quarter of car insurance policyholders do not shop around for the best car insurance deal on their new vehicle.
Sainsbury's Car Insurance revealed these figures and claimed that they could save motorists up to £180 each with competitive car insurance premiums.
Many motorists ignore the well-known fact that car insurance premiums differ depending on the policyholder's car, according to Joanne Mallon, Sainsburys, Car Insurance manager.
"Motorists should be aware that doing nothing and just sticking with the same provider when changing their car could mean they end up paying over the odds," she said.
Research company Consumer Intelligence recently found that Sainsbury's Car Insurance consistently came out in the top quarter of competitive car insurance providers.
Sainsbury's Car Insurance also offers added benefits like full no claims protection and a courtesy car.
Sainsbury's Bank has been named as the "Best Overall Provider" for the second successive year in the 2004 Your Money Direct Awards.
Sainsburys Bank opened in 1997 as a joint venture with Halifax Bank of Scotland.
The bank has a range of available financial services, including insurance, loans, credit cards and savings accounts.




