Baffled by road tax

I own a 2003/53-plate Mercedes-Benz SLK 230. The CO2 emissions are 226g/km, according to the registration document, but I'm baffled as to how much tax I will have to pay from 2010. I've heard so many conflicting reports! Can you help?
Peter Thompson

Because your car was registered between March 1, 2001 and March 23, 2006, you'll pay 245 a year for your tax disc from April 2010.

Bands L (226g/km-255g/km) and M (over 255g/km) only apply to cars registered after March 23, 2006. If your Mercedes had first been registered later, you'd have had to cough up 425 a year.