Average sale prices decreased by 3.5% from £5,588 to £5,391 month-on-month, according to the latest report from the National Association of Motor Auctions (NAMA).
Sales volumes for September were up by 12.6% in comparison to August 2015, in line with the seasonal trends during the 65- number plate change.
In terms of a year-on-year comparison, vehicle auction sales rose by 13.2% from 99,165 in September 2014 to 112,888 in September 2015.
The percentage of vehicles sold first time in September increased from 84.1% in August 2015 to 85.4%, an increase of 1.5%.
The price premium for vehicles sold fell from £350 to £300, and the average days on site decreased to 7.3 from 8.2 days.
Three out of five market sectors saw price growth on the equivalent month in 2014 with no change in the budget sector and the late and low category showing a fall of -1.6%. There has been a significant number of budget vehicles sold at auction during the month and NAMA said this masks some of the value achieved in other sectors.
Paul Hill, NAMA chairman, said: “The September plate change has driven volume up through the month with values compared to August 2015 starting to decline. Available volume in auction was up significantly at the start of October and conversion rates have lowered.
“It is anticipated that volumes will continue to grow in during the month as fleet returns and part exchange volume continue to fill the lanes. Values will come under mounting pressure during October and will see an additional fall.
“Vendor auction partners need to be close to the market changes and advise swiftly on the rostrum and council at the pre-auction briefing to ensure days to sale remain down and the best values are achieved on the day.”