The http://www.whatgreencar.com/ website came to our rescue again, with it's green car selector. You enter your requirements - in our case we wanted a petrol-driven small family car (but you can choose sports cares or SUVs or executive cars amongst other choices, and you can have diesels, hybrids, electric or LPG as fuel choices). It gave us a list of possible cars, but the greenest of the choices it presented was a VW Polo. So that's what we've bought, a little red green car, to replace our old road hog.
I've included the Environmental Impact charts so you can see how much "greener" the Polo is compared to our old MPV.