Mike Hawes, SMMT chief executive, said: “During a torrid year, the automotive industry has demonstrated incredible resilience, but this is not a recovery. Despite the boost of a new registration plate, new model introductions and attractive offers, this is still the poorest September since the two-plate system was introduced in 1999.
“Unless the pandemic is controlled and economy-wide consumer and business confidence rebuilt, the short-term future looks very challenging indeed.”
However, the decline is not entirely down to motorists reining in their spending, according to trade group the National Franchised Dealers Association.
It said that dealers had experienced “strong” demand with “high levels of enquiries”, but supply problems had held back a number of manufacturers so they had been unable to get cars to buyers.
Sales of cars to private motorists, which represent roughly half of the total, were down 1.1pc in the month, while those to fleet buyers such as hire firms were 5.8pc lower.
So-called “alternative fuel vehicles” such as electric and hybrid cars continued to grow in popularity, making up just under a third of all registrations during September, up from just over a 10th a year ago.