The UK car new market fell by 20.5% in September year-on-year, according to data from the the Society of Motor Manufacturers and Traders (SMMT).
The sharp decline is due to the ongoing impact of the WLTP emissions regulations that were introduced on 1 September. These regulatory changes mean many manufacturers are still catching up with testing under the new regulations, meaning not all car variants are available.
By comparison, August car registrations saw a massive rise of 23.1% year-on-year as manufacturers tried to shift as much old stock (which would not adhere to the new regulations) as possible.
In September, 338,334 vehicles were registered, down around 87,000 on the previous year.
Diesel sales saw the sharpest decline, dropping 42.5% compared with September 2017, while petrol registrations fell 6.7%. Diesel now holds a market share of 29%.
Alternatively fuelled vehicles, which include hybrids and electric cars, rose 3.9%. AFVs now hold 6.9% of overall market share, up from 5.3% last year.
MPVs and specialist sport cars were hit hardest, down 54.8% and 50.9% respectively, while the only segment to register growth was luxury saloons, up 3.5%.
Volkswagen, which has openly admitted struggling to get all of its vehicles through testing in time, was one of the worst hit. Its car registrations fell 55.18% year-on-year while VW Group-owned Porsche also suffered. Its figures fell 67.85% compared to September 2017.