I received renewal notification to tax the car when it was about to run out. I had the MoT done and I noticed on the renewal notification that the annual tax was £215. It mentions engine capacity/CO2 178g/km. I drive a Mercedes-Benz 220CDI diesel. My son also drives Mercedes 220CDI Diesel Blue-Efficiency, which he bought last year and had paid £170 for the tax. Has my car tax gone up because of CO2 emissions?