Sales jumped by 25.4 per cent to 443,265 units last month, on the back of a 29.4 per cent leap in private registrations as retail customers accounted for 243,049 new cars, including a huge increase in retail diesel sales.
Fleet and business registrations were close behind, rising 16.6 per cent and 39.1 per cent respectively, the year's strongest performance from the market. Sales to fleets with 25-plus vehicles in September totalled 156,780 units, while the sub-25 fleet market bought 43,436 units.
The '51'-plate boom has pushed year-to-date fleet sales to almost the same level as last year, with large fleet sales 0.2 per cent lower than the same period last year, at 812,085 units, and business sales down 2.4 per cent to 176,407.
With the launch of the carbon dioxide-based company car tax fast approaching, fleet diesel sales followed the car market into overdrive, rising 58.8 per cent, to 37,790, in a total diesel market up 70.5 per cent at 80,069.
Manufacturers reported September increases in sales ranging from 21 per cent to a massive 409 per cent fleet sales increase for Rover, with 1,039 units.
Topping the September diesel sales league was the Vauxhall Vectra, at 2,856 units, up 250 per cent on last year, followed by the Ford Mondeo, at 2,843, up 41.7 per cent and the Volkswagen Passat, up 150.2 per cent to 2,567.
During September, 24.1 per cent of fleet sales were diesel, pushing the year-to-date fleet diesel market up to 26.6 per cent of the total fleet market.
Ford led the overall fleet sales league table last month, with 30,069 sales, with the Ford Focus taking its regular place at the top of the league, with 11,140 sales. However, despite rocketing retail sales, Ford's fleet sales were down 1.1 per cent last month compared to September 2000.
Vauxhall sales were up 21.7 per cent in September compared to last year, at 28,362, with Vectra sales up 30.8 per cent at 9,314 to achieve second place in the fleet sector, ahead of Ford's Mondeo in third.
Peugeot held third place in the overall sales figures, with 13,435 sales, up 8.3 per cent on September last year, while Renault was down 17.8 per cent at 11,145. Volkswagen held fifth place, with 10,810, up 39.4 per cent, followed by Nissan at 9,155 (up 43.4 per cent), Fiat sold 6,967 (up 91.6 per cent), Citroen up 41 per cent at 6,903, BMW down 6.2 per cent at 6,480 and Toyota up 32.4 per cent at 5,619.
For the year-to-date, the Ford Focus holds a commanding position, with 73,224 fleet sales, nearly 20,000 units ahead of nearest rival, the Vauxhall Astra, with 55,254 sales, followed by Ford Mondeo (52,029), Vauxhall Vectra (43,488) and Renault Megane (34,472) respectively.
In the full market, Ford has sold 180,024 units, up 2 per cent for the year-to-date, while Vauxhall has sold 158,734, up 0.3 per cent over the same period.
Rivals Peugeot and Renault show a 9 per cent year-to-date fall in sales, at 69,626 and 66,750 respectively, while fifth placed Volkswagen is up 24.1 per cent at 54,615.