Manufacturers registered 99,299 cars to fleets in November, a rise of 5.1% compared to the previous year, according to figures from the Society of Motor Manufacturers.
It meant the fleet sector accounted for 53.9% of the market, as the share of cars bought by private buyers dropped 1.8 percentage points to 42.4%.
Business customers registered 6,735 cars to take 3.7% of the market.
Overall, 184,101 new cars were registered in the UK in November, with the market increasing by a steady 2.9%.
The growth has helped deliver more than 2.5 million new cars on to British roads so far this year – the first time the milestone has been reached in November.
Demand for alternatively fuelled vehicles (AFVs) remained strong in the month, growing 25.1% to 6,663 units, representing 3.6% of the market – the highest ever achieved.
Petrol registrations grew 7.9% to 88,541 units, while diesels just edged ahead on market share with 88,897 vehicles registered, a fall of -2.9%.
Superminis continued to be the most popular body style – making up more than a quarter (29.7%) of all cars registered in November, followed by small family cars and SUVs.
Executive and city cars enjoyed the biggest growth, up 27.7% and 25% respectively.
Mike Hawes, chief executive, of the SMMT, said: “Our industry continues to make vehicles that are ever safer, more refined, more efficient and more enjoyable to drive – and the latest advanced technology and cutting-edge designs are continuing to attract buyers into showrooms.
"It's encouraging to see that alternatively fuelled vehicles, although still a small proportion of the market, have seen strong growth this month achieving a record market share.
"Long-term Government support and incentives are essential if these vehicles are to command a larger market share in the future.”