Since the recession started, environmentalism has pretty well slipped off the agenda of the average motorist. Most people want low fuel consumption and low road tax, and if that happens to involve low CO2 emissions, that is OK, but the CO2 element is not particularly important.

However, there are two reasons why the environmental issue is dormant, not dead. Firstly, when (although these days it seems more a question of if) we get back to solid economic growth, the environment will come back on to the agenda. Secondly, there will soon be a lot of cars with completely different approaches to low emissions and people are going to start wondering which ones make sense.

Up to now, hybrids have been broadly comparable with the best equivalent diesels. The last-generation Prius had a CO2 figure of 104g/km, now reduced to 89-92g/km depending on the version.

That compares to the best lower-medium diesels at 98g/km and the best upper-medium diesels at 109g/km. However, next year Toyota will introduce the first plug-in Prius with a lithium-ion battery pack, with an expected CO2 figure of 59g/km. That is a genuinely low CO2 figure and thus will be eligible for the Government’s £5,000 grant (as an aside, does that mean the plug-in version will cost no more than the current Prius?).

However, that is still 59g/km more than the Nissan Leaf, right? Not necessarily. The electricity for the Leaf has to be generated, and most UK electricity is generated from fossil fuel. So how much CO2 is generated to power the Leaf?

According to the independent National Energy Foundation, the electricity needed to charge the Leaf’s 24kW/hr batteries produces 13,000g of CO2 and gives a range of 160 km. Dividing 13,000 by 160 gives 81g/km of CO2 for the Leaf.

An alternative calculation from the US Environmental Protection Agency reckons the Leaf does the equivalent of 118mpg. That would be approximately 60g/km of CO2. So the Leaf figure is 60-80g/km depending on your calculation.

Meanwhile, Kia has introduced the (admittedly smaller) Rio 1.1 diesel with 85g/km of CO2, which shows that conventional engines have not given up the fight yet. Both electric vehicles and, to a lesser extent, plug-in hybrids make a major impact on local air quality, as power stations are located well away from urban areas, but the overall CO2 savings are not compelling.

So are the car companies being cynical in promoting electric vehicles that do not save major amounts of CO2? Not at all. They have fulfilled their side of the bargain – now it is up to governments to generate enough clean electricity to power them.