New car sales slumped 21 per cent year-on-year to 330,295 units last month - marking the weakest September since the twice-yearly plate-change was introduced in 1999.

September is the second biggest sales month of the year behind March, accounting for about 17 per cent of total annual volume, but this year the difference between the two plate-change months stretched to 120,000 units, the SMMT said.

Sales during th...