There's no doubt that the Toyota Prius is the most well-known green car in the world, a fact that's as often attributed to the car's distinctive styling as it is to the car's impressive fuel efficiency.
Toyota has already set a high benchmark with the new 1.8-litre petrol hybrid Prius, and it sees plug-in technology as the next ecological step.
The Japanese giant is also not such a major player with diesels, and while it did a deal with Isuzu in 2007 to develop a new aluminium-block 1.6-litre diesel, a unit that could be used to power a diesel hybrid Prius, production of that engine is not scheduled to begin until 2012 at the earliest
We already make a diesel hybrid truck in Japan, but in order to mass-market diesel hybrids we need to make the exhaust emissions much cleaner, and that requires development. You have to combine this clean emissions technology with the hybrid system cost, so that means that, currently, it's a very high-cost powertrain for us. So for Toyota, it will take many more years.
A plug-in hybrid version of the new Prius, with a lithium-ion battery pack, is due in Japan before the end of the year. The UK will also get to see the car, probably in 2010; Toyota may confirm that plan within the next month.
The numbers are small, though; Toyota’s aim is to do a run of 200 plug-in cars for Japan, then a further 300 for the US and Europe.