AMAP explained
Authorised Mileage Allowance Payments are where employers reimburse employees for business miles travelled up to the maximum 40p per mile rate, with payments over this rate being taxable.
The current AMAP rates of 40p for the first 10,000 business miles and 25p thereafter, are not normally extended to the employee in full. If for example, you gave the average mileage rate of 9p for a diesel car and 12p for petrol the employee would claim the difference between the 40p and 25p back from the Inland Revenue.
In the 2007/2008 budget, the government announced it is considering the case for changing the structure of AMAPs to 'align the tax and National Insurance treatment and to ensure that rates and thresholds are set at an appropriate level to promote environmentally friendly business travel'.