Toyota‘s latest Prius is not just its most important fleet car of this year, but the brand’s most important car for years.

The previous generation was almost unchallenged in the low CO2 market when it launched in 2004, but now it faces serious competition from Honda‘s Insight and a spate of highly efficient diesels. As a result, it had to do something special to be seen as more than just a facelift, and it has succeeded in almost every way.

Claimed combined fuel consumption of 70.6mpg is impressive on its own, but then consider that, thanks to the completely redesigned high-power battery, the Prius claims it can produce the same figure around town. It allows the driver to choose to run on electric power alone for nearly one and a half miles at speeds up to 31mph. On an eco driving challenge on the launch we managed 85mpg, and still didn’t come out top.

The other key figure is CO2 emissions. The entry-level car on 15-inch wheels manages just 89g/km, while this T-spirit emits 92g/km thanks to 17-inch rims. This is matched only by the tiny Smart diesel, and no other car of this size comes anywhere near. The new Prius is a large lower medium car and its only hybrid rival, the Honda’s Insight, only manages to come down to 101g/km.