In terms of annual volumes, that makes 2013 the worst year since 1995 (when the European Union consisted of 15 countries), and the worst ever since ACEA began the series in 2003 with the enlarged European Union (which now encompasses 28 nations).
The group said that results differed significantly across European markets over the last 12 months. While the U.K. recorded double-digit growth in new car sales of 10.8 percent and Spain posted a more moderate upturn of 3.3 percent, countries like Germany and France posted declines of 4.2 percent and 5.7 percent respectively.
(Read More: Why the UK's auto industry remains crisis free)
Overall, the EU market recorded a total of 11,850, 905 new cars or 1.7 percent less than in 2012.
Carlos Da Silva, manager for European vehicle sales forecasts at IHS Global Insight, told CNBC that although the December sales increase was "quite an achievement" given the overall economic and social climate in Europe, "one must also realize how low, in absolute terms, these volumes are: the lowest since 1995 the ACEA says."
"The misunderstanding would be to consider that, from now on, after four months of continuous growth, the EU market is out of the woods and back on track as if nothing had happened," he told CNBC on Thursday.
"The recent good results have been welcome but were they so good actually? After years of collapsing sales, pent-up demand has definitely started releasing in 2013 but there was also a fair share of artificially-fed demand," he said, citing U.K. market sales growth as being " due to very good bargaining conditions" or Spanish growth thanks to the country's car-scrapping program.
"In 2014, the EU market is set to make its come back…But, at the same time, we caution that the recovery road might be very slow and staggered. As evidenced by the fact that we expect car sales volumes to pass 2008 volumes again only by the next decade," he warned.
- By CNBC's Holly Ellyatt, follow her on Twitter