Among vehicles acquired for its customers, diesels have increased from 51% in the period October 2001 to March 2002, to 64% in April to September 2003.
Mike Waters, head of market analysis at Arval PHH, believes changes to the tax regime have prompted the surge in the number of diesels being chosen.
He said: 'The tax changes that came into force in 2002 made diesel cars a lot more attractive, as their lower carbon dioxide emissions have generally resulted in lower tax bills.'
However, Waters believes the surge in diesel sales could have an adverse effect on the used car market. He said: 'When these cars reach the end of their leases there will be a lot of second-hand diesels on the market. This is likely to result in even more pressure on the sector.'