Business sales so far this year total 209,080 units, an increase of 7.6% on the same period last year, but fleet sales to companies with larger car parcs have fallen by 2.2%, to 836,178 units.
For the month of September, fleet sales were down 4.3% to 161,248 units, while business sales were up 10.4% to 53,992 units, when compared to the same month last year.
Combined, the two markets for the year-to-date account for 50.4% of the market and for September, 49% of the market.
In terms of manufacturers, the Vauxhall Corsa saw the most registrations in September, the first time since February 2000.
Figures produced by the Society of Manufacturers and Motor Traders (SMMT) show the Ford Focus has slipped to second place after 40 consecutive months at the top but it is still the best selling car in the total market for the year to date.
The Ford Mondeo has topped the diesel table for both September and the year-to-date and figures also show that total diesel registrations are up for the 36th consecutive month, up 20.8% in September and 16.9% for the year-to-date.
SMMT chief executive Christopher Macgowan said: 'As the outlook for consumer spending remains uncertain, the growth in new car registrations demonstrates the strength of confidence in the UK market.
'Private buyers accounted for more than 50% of registrations in September, snapping up the new '53' number plate and taking advantage of great deals offered by franchised dealers.
'As competition in the UK market intensifies and prices continue to fall, consumers are clearly benefiting and driving the market towards a healthy year-end total.'