What Car? Q&A - Which green car should I buy?
A: The Polo BlueMotion emits just 99 grammes of CO2 every kilometre and particulate emissions are also low, thanks to a special filter. You're right, though - nitrous oxide (NOx) emissions are fairly high.
You could consider a small petrol car, such as the 1.0-litre Citroen C1, Toyota Aygo or Peugeot 107 (they are essentially the same car). CO2 outputs are slightly higher at 108g/km, but NOx emissions are 20 times lower than the Volkswagen's.
All these cars are smaller than the Polo, but since you don't need the space, that shouldn't be much of a problem. They are also a lot cheaper - the Toyota is the cheapest and starts at just £6950, or less with a bit of haggling.
If you can hang on until February, Smart is launching a 0.7-litre diesel Fortwo that emits just 88g/km of CO2. There's no word on NOx and particulate emissions yet, but it should do a whopping 86mpg.