Update - 10.19am: Insurers are denying they have dropped their prices because of a clampdown on cartels.
Car insurance policies are down by 14% - the biggest decrease since a surge in bills three years ago.
However, the CEO of Insurance Ireland Kevin Thompson denied that the investigation was responsible for reducing premiums.
He said: "Premiums are a direct function of claims and until we get stability in the claims environment and we reduce the cost of claims, then you've got a chance of altering what premiums are offered.
"There is nothing to say that an EU ongoing investigation has anything to do with premiums."
Earlier: Car insurance costs are coming down but it could be a while before motorists see an improvement in their bills.
New figures from the Central Statistics Office for August show there has been a 14% drop in prices, the most dramatic decrease since costs began rising three years ago.