AVERAGE petrol prices have fallen to their lowest level for nine months but remain stubbornly higher than last year, the Automobile Association has found.

Petrol pump prices in Scotland now average 132p per litre, marginally lower than the UK average price and down 1.4p from November, reaching a level last seen in March.

But the AA's monthly fuel report pointed out this was still significantly higher than 2010, when the average price of petrol for the year was 117p.

The average diesel price for 2011 was 139p, up from 120p the previous year.

The AA said the increased costs would have added £420 to the annual fuel bill for a family with two petrol cars and £15.50 to the cost of filling up a commercial van with an 80-litre tank.

"As more severe winter conditions push up fuel consumption and families contemplate the cost of Christmas travel, it will anger many that pump prices remain artificially high in so many places," said Edmund King, president of the AA.

"This is simply because there isn't the transparency in the fuel market to indicate where prices should be. Only when such glaring regional disparities as we've seen this month emerge or prices between neighbouring towns vary by as much as 4p a litre do motorists know that something is wrong."

The latest changes have also pushed up the gap between petrol and diesel, which is now 8.6ppl more expensive than unleaded, an increase of 1.4p on November. The increased differential has added another 10,000 miles to the point at which motorists can expect to recoup the typical £1500 higher purchase price for diesel cars, the AA said.

It found there was a "north-south" divide between pump prices in London and the south- east and northern England.

Across London and south-east England, the average price is 133.55p for a litre of unleaded compared with 131.63p across northern England.

The gap between fuel prices charged at competing supermarkets has also grown to 1.8p – the biggest gap recorded this year, the AA found. It said some independent retailers were undercutting supermarkets by as much as 2p but complained these were few and far between.

Mr King said: "If it is a case that some of the cash consumers save at the supermarket checkout is clawed back at the pump, it is a risky strategy.

"AA research shows that 28% of its members budget a set amount on fuel, rising to 40% among less well-off drivers.

"Getting to and from a superstore at the end of the week can easily consume a litre of fuel, and that may be enough to make some customers shop closer to home. We are also seeing a growing number of independent retailers taking the opportunity to undercut supermarket rivals by as much as 2p a litre. Drivers just wish there were more."

Mr King added: "Although falling oil prices have brought prices back to where they were in the spring, the relief isn't that great for rural and lower-income drivers.

"For many, this year has been like 12 rounds in the ring with a heavyweight boxer.

"Yes, the tempo of the pump price punches may have lessened, but drivers are still being pummelled. Some have been knocked out for good."