Car insurance premiums have increased by £20 since July, according to the AA's British Insurance Premium Index third quarter figures.

Both average comprehensive and non-comprehensive premiums have risen more than 3%, although the AA says drivers can save about a third by shopping around.

The average comprehensive premium is about £580 and non-comprehensive is £576, but the cheapest comprehensive is £371 and non-comprehensive is £383.

In the past year the greatest rise in car insurance has been in Oxford's postcode OX1, where the average premium has risen by 32%. Southend-on-Sea's SS1 postcode has enjoyed the smallest rise of 9%.

These figures are based on prices quoted for a late 30s couple driving a Ford Escort, with full no claims bonuses and clean licences.

AA insurance director George Lowe said costs were increasing because insurers were keen to make profits after years of taking losses to gain market share.

"As they move to break even, in theory, this means that few insurers can justify above-inflation rises beyond the middle of 2001," Lowe said.

However, he said premiums would continue to rise steadily as more drivers made claims for same-size replacement cars and for compensation for minor injuries, pushing up the cost of payouts.