As the used car market prepared for a flood of defleeted cars as a wave of new '52-plate cars were handed over to company car drivers, the average value of used cars fell by 9.3% compared to the same period last year.
Compared to a fall of 3.7% during July, the price collapse wiped tens of millions of pounds from used car values, but industry experts say it had to be expected as the second bi-annual plate change approached.
Despite growing demand for economical cars, superminis were worst hit, with prices down 11.4% year-on-year. Lower medium models were down 10.5%, a fall matched by upper medium vehicles, while sports cars were down by 9% and MPVs fell 8.4%. Executive cars and 4x4s fell by 3% and 2.2% respectively, according to the CAP Index, which monitors the value of used car values for three year old vehicles that have covered 30,000 miles.
But Ramesh Notra, CAP Economics editor, said the industry could actually take the fall as good news.
He said: 'Although the figures show an apparently accelerating year-on-year fall in used car values, the reality is that the used car market has performed better during August than many in the industry had expected.
'This is a blip which will be ironed out next month with the change in three-year-old car letters from 99T to 99V. A shortage of stock has kept prices cushioned. However, that picture could change this month with a massive influx of part exchanges.'
The findings also throw doubt on recent research that claims that unprecedented demand for used cars could actually push prices up.
By contrast, new car prices were up 2.9%, remaining the same as last month.
Demand for lower medium cars has pushed prices in that sector up fastest, by 6.1%, while upper medium models were up by 2.9%. Only 4x4 prices fell, down 0.5%. Notra added: 'This reflects the buoyancy of the new car market. While sales remain high, pressure on manufacturers to reduce list prices remains low.'