It was the third consecutive year of decline, and the SMMT expects that trend to continue in 2020.
Those expectations are largely due to weak consumer confidence and confusion over clean-air legislation.
Car industry are facing serious challenges adapting to new emissions legislation.
New rules will require a massive expansion in the use of electric and hybrid cars.
The SMMT’s figures show a total of 2.31 million new cars were registered in 2019, down 2.4% from the year before.
Since reaching a record high of 2.69 million vehicles in 2016, the market has been steadily contracting.
A key factor has been the collapse in demand for diesel-powered cars, which fell by 22% compared with 2018.
Where once they accounted for half of all new cars sold, now they make up just a quarter of the market.
The SMMT says uncertainty over future air quality rules, and in particular over potential restrictions on diesel vehicles entering city centres, has left consumers confused combined with political uncertainty and a general fall in consumer confidence.
Electric and hybrid cars
One area in which sales have increased dramatically over the past year is the market for “alternatively fuelled vehicles”, in other words electric cars and hybrids. Which has rised by more than a fifth. Registrations of pure-electric cars were up 144%.
Sales of electric and hybrid vehicles will still need to rise very substantially.