7 per cent less CO2 than models sold in 1997, according to the SMMT report New Car Registrations by CO2 Performance.
The figures also revealed a 1.2 per cent drop between 2004 and 2005.
The UK's greenest car last year was the petrol/electric Honda Insight followed by the Toyota Prius, which is also a petrol/electric hybrid. The Citroen C2 diesel was third.