Yes, I would expect it to be taxed if it is just another salary element. How certain are you that it isn't being taxed? The tax deduction wouldn't appear as a separate deduction- it would just be factored in to your overall tax deduction.
However if it is a payment to cover your expected business mileage then there may be no tax due, depending on your actual business mileage.
thanks for your answer
i had payments from tax year 07-08 of 500 each month included for car allowance in my wages but no tax deducted by my employer because just been sent a under payment tax demand for this amount also i was claimg back mileage i no longer work there