As you'd expect with this sort of question, there is more than one answer. The short answer is that the best way to help the environment is to not own a car - they create pollution when manufactured and continue to pollute for the rest of their days.

Obviously this isn't practical for some and certainly undesirable for the majority of us. There's little doubt that a hybrid is significantly more enviromentally friendly than a conventional car. The power to the electric motor is mostly generated under deaccelaration or braking so is using energy that would otherwise be converted into heat.

If you want to take it right back to brass tacks then you could ask if manufacturing the electric motor and associated gubbins creates more polution than the car will save - I don't have exact figures to hand (as they don't exist!) but common sense would suggest that overall, a hybrid will pollute less in its life than it made to manufacture.

Honda claim (on their awful website) that the Civic IMA saves 10 tonnes of carbon dioxide over 100,000 miles. I assume they mean compared so a similar car as opposed to a train but even so, that's a fairly impressive claim.