The total amount of vehicles sold in the UK was 2.37 million, the lowest figure for the past five years.
The biggest decline was seen in the diesel sector, down 29.6 percent on the previous year. According to the SMMT, anti-diesel comments and negative fiscal measures took their toll on diesel vehicles market.
The growth of registrations of petrol and alternatively fuelled vehicles rose by 8.7 percent and 20.9 percent respectively, failing to offset the overall shortfall.
Meanwhile, the SMMT claimed UK's pace of growth on plug-in cars is now falling significantly behind the EU average, given that the government has reduced incentives.
"A second consecutive year of substantial decline is a major concern," said Mike Hawes, the SMMT chief executive, adding that "the industry is facing ever-tougher environmental targets against a backdrop of political and economic uncertainty that is weakening demand."