The industry market expectations were beaten by 3% or 5,000 units.
Despite the rise in May, volumes were still down by 46,438 units, 4.3%, over the first five months of the year.
The supermini market posted an impressive recovery in the month, with volumes up 6,955 units on their 2005 level. The MPV, luxury saloon and sports car markets also rose in May.
The Ford Focus remained the best selling model in both the overall and diesel market for the month and year-to-date.
Fiat once again posted strong growth, thanks to the new Grande Punto lifting their year-to-date performance.
Diesel penetration hit a record high for the month at 37.9%. Over the year-to-date, the diesel market share rose to 36.9% with the year-end forecast to hit 38%.
The annual running total for diesel registrations exceeded 900,000 units in May, after a 4% growth in the month.
The Ford Focus has been the best selling diesel model in every month of 2006.
"Franchised car dealers are still reporting a very patchy climate - many have seen falling registrations this year, but there are others bucking this general trend,’ said Sue Robinson, director of the Retail Motor Industry Federation’s (RMIF) National Franchised Dealers Association. She added: "There appears to be a number of factors impacting consumer behaviour, but, overall, the economy seems to be the biggest issue. The imminent decision on interest rates is also influencing the market. "Dealers are hopeful that June will continue the slight improvement shown in May, before the onset of the traditionally low sales months of July and August."