What are advisory fuel rates? 

These rates are issued by HMRC on a periodic basis and can be used to reimburse employees for business travel in company cars, or if an employee needs to repay the fuel used for private travel in a company vehicle.

The rates issued are not statutory, however there are implications if rates are used which differ to the advisory ones provided. 

If higher amounts are used per mile when reimbursing employees for business travel in a company car,  you have to treat anything that exceeds the advisory fuel rate as a taxable profit and as earnings for Class 1 National Insurance purposes. There will be no fuel benefit charge implication if the mileage paid is for business travel only. 

If you need to repay your employer for private travel in a company vehicle, and you use a rate that is less than the advisory fuel rate, the difference may be considered a taxable benefit to you as the employee and may incur a fuel benefit tax charge.