Numbers top 2.63 million after a record December though Volkswagen saw volumes slip last month after the diesel emissions scandal.
New car sales reached an all-time high last year, according to new industry figures.
The Society of Motor Manufacturers and Traders (SMMT) said 2.63 million cars were registered in the UK in 2015, up 6.3% on 2014. It beats the previous record of 2.58 million set in 2003.
Last month also broke the record for December sales, up 8.4% on the year before at 180,077.
SMMT chief executive Mike Hawes said: "The new car market defied expectations in 2015, hitting an all-time record driven by strong consumer and business confidence.
"Buyers took advantage of attractive finance deals and low inflation to secure some of the most innovative, high tech and fuel efficient vehicles ever produced.
"The past four years have seen a remarkable period of sustained growth, and the outlook remains positive with every reason to expect the market to hold broadly steady in 2016."
The market has been recovering after annual sales dipped below two million in both 2009 and 2011.
There were 43 consecutive months of year-on-year growth until a dip in October but this was followed by a 3.8% rise in November and a bumper December.
In the wake of the diesel emissions scandal, Volkswagen car sales fell by 0.4% in December compared with the same month in 2014. The brand had experienced a 20% decrease in registrations in November.
For the year as a whole Volkswagen sales were up by 4.2% compared with 2014.
There were mixed results for other brands owned by the Volkswagen group last month, with Seat down by 46.4% but Audi up by 14.1% and Skoda by 4.2%.
The 2015 market share of all diesel cars fell from 50.1% to 48.5%.
Mr Hawes said: "There has been a lot of comment and concern around air quality and diesel.
"I think the fact that the market for diesel has held up demonstrates that, for a lot of consumers, they are still driven by fuel economy and diesel offers better fuel economy."