For cars registered on or after 01/03/2001, if the CO2 emission is less than 100g/km, your road tax falls in Band A, which does not require road tax. You can find the CO2 emissions of your car by checking your V5C (vehicle registration certificate) or via DVLA's Vehicle one service. Since the technology is improving, there are more and more cars have low CO2 emissions. You can find a list of cars that do not need road tax here.

You need to pay road tax if your car is registered before 01/03/2001. You need to pay £130/year if the engine is less than 1549cc; £215/year if its over 1549cc.