Full-year sales figures supplied by the Society of Motor Manufacturers and Traders (SMMT) show Vauxhall supplied 221,806 cars to fleets during 2003, compared with Ford's 213,947 units.
It marks the first time Vauxhall has gained first place in the fleet car market from Ford, which responded by commenting 'profitability from our fleet sales is not necessarily maximised by chasing outright or short-cycle volume targets'.
Jubilant Vauxhall fleet executives say they are confident of maintaining the lead position this year.
The manufacturer is one of only two in the fleet sales top 10 which increased its sales last year. Toyota is the other, with sales up by 1.7% on the previous year.
Total fleet sales were down by 2% but business sales to sub-25 fleets were up by 8.3%. Last year's best-selling fleet model was again the Ford Focus, which sold 91,234 units, although this represents an 11% drop on 2002's sales. Overall, Ford was the UK's best-selling manufacturer, achieving sales of 378,942 units.
The SMMT figures show that total new car sales, including those to private buyers, achieved record figures and were up 0.6% on the previous year.