Plans to price car insurance by the mile, as proposed by the Institute for Public Policy research, may not be workable, the AA says.

The institute suggested that mileage-based premiums could reduce insurance costs for low-income motorists who driver fewer miles.

AA spokeswoman Rebecca Hadley said the AA, the UK's biggest car insurance broker, already offered discounts for drivers with very low mileage.

"However, this kind of insurance is more suited to occasional-use cars, not for the vast majority of cars that are used for commuting and ferrying the family around," she said.

"The age and experience of the driver and the make and model of the car are currently the biggest factors in pricing insurance cover and will remain so until a better method of calculation is found.

"The total number of miles driven is not the whole story. Drivers are ten times more likely to be involved in injury accidents on the local school run than on a long holiday trip on rural motorways."